• French officials say more than 80 dead in Nice attack.
• More than 100 people injured, 18 critically, after truck ploughs into crowd celebrating Bastille Day.
• Man behind wheel of truck fired shots into crowd after crash.
• Driver shot dead by police.
The driver of a large truck mowed down hundreds of revellers at Bastille Day celebrations in Nice drove in a zig-zag fashion at about 70km/h to hit as many people as possible, say witnesses.
The truck, laden with grenades and weapons, ploughed into a crowd celebrating Bastille Day on the Promenade des Anglais during a fireworks display.
French Interior Minister Bernard Cazeneuve has confirmed 80 people are dead and 18 are in intensive care.
"Our thoughts go to all the people of Nice who tonight are traumatised and plunged into a great state of worry," he said during a press conference.
Cazeneuve said the police were working to identify the man behind the attacks were trying to establish if he had any accomplices.
"We are at war with terrorists who want to strike us at every cost and who are extremely violent."
French president Franois Hollande earlier said: "France has been struck on the day of her national holiday, the symbol of liberty.
"We show our solidarity towards the victims and their families.
"All means are being deployed to help the wounded," he said.
France is being threatened by "Islamic terrorism", he said, and had to "demonstrate absolute vigilance".
The nation had to show "determination that is unfailing".
"France is horrified by what has taken place, this monstrosity of using a truck to deliberately kill dozens of people who had come to celebrate 14 July.
"France is afflicted but I assure you she is strong and she will always be stronger than the fanatics that want to strike her today."
Hollande said it was an act of terror that "cannot be ignored" and this is "of absolute horror and it is clear that we have to do everything to ensure that we can fight against the scourge of terrorism".
He said they needed to see if there were accomplices involved in the attack.
"Human rights are denied by fanatics and France is quite clearly their target"
"Numerous measures have been taken, measures which have been considerably enforced and strengthened, but we have to because this is holiday time, we have to increase further our level of protection."
"I've also decided to appeal on the operational reserves...We can deploy them where we need them, and in particular, for the control of borders"
"I announced yesterday morning that a defense council would take place tomorrow. It will study all measures that we've already taken and which I've just announced. It will thus make it possible to have a deployment of all necessary staff at all sites and all towns and cities where we need them for protection and vigilance"
The French government has called for the cancellation of all events scheduled in Nice in the coming days.
Reports from Nice say a 31-year-old French-Tunisian man was driving the truck.
AFP reported identity papers of a French-Tunisian were found in the vehicle.
According to The Guardian, reports said the driver was known to police, but not for terrorist-related activity.
At least 100 people were injured and many are crowding the lobby of luxury hotel Negresco, which has been turned into a field hospital.
The Daily Telegraph is reporting that three Australians have been injured in the attack. Foreign Minister Julie Bishop confirmed all three suffered minor injuries while fleeing the horror.
One of the injured Aussies was a woman on a Topdeck tour, the tour company confirmed.
Helicopters were reportedly landed on the Promenade des Anglais.
Images from the scene showed about a dozen people lying on the street, some being attended to, and videos posted online showed people fleeing in panic. Some were screaming, many were pushing children in pushchairs.
The truck mowed people down over a distance of approximately 2km until it was stopped on the promenade, Le Monde has reported. It was travelling at an estimated 60-70 km/h.
Witnesses say the truck mounted the footpath and piled into everyone the driver could see, ramming over those who tried to run away.
One witness, Roy Calley, told the BBC that there were "thousands of people on the promenade" when the incident happened.
"The police have completely taken over the city, the promenade has now been closed down. Everybody was physically pushed away from the site and told to get back in no uncertain terms by the police.
"I live 200m from the promenade and it took nearly one hour 30 minutes to get back to my flat because all the roads have been closed down."
Another eyewitness told BFM TV: "Everyone was calling, 'Run, run, run there's an attack run, run, run'. We heard some shots. We thought they were fireworks because it's the 14th of July.
"There was great panic. We were running too because we didn't want to stick around and we went into a hotel to get to safety. "
Tony Molina told CNN that he watched the chaos from his hotel room on the promenade.
"There was still a crowd of people and then you just see this big white panel truck, I couldn't see the driver, but it just kept going at different angles from left to right at 25 to 30 miles [40-50km] an hour," he said.
"People were screaming and running. There are still people I am looking at right now that are near their deceased family members.
"I work in homicide and I've never seen anything like this. It's unbelievable."
A witness told AP he saw the truck's driver get out of the vehicle with a gun, and start shooting into the crowd.
A journalist from the Nice Matin newspaper said there was "a lot of blood and without doubt many injured".
Another witness said: "We saw a white lorry which drove directly into people on the Promenade des Anglais. A gunman fired into the crowd before being shot by police."
The French Interior Minister has confirmed the truck driver is dead.
Police sources said weapons and grenades were found in the truck.
Officials have activated France's Plan Blanc emergency response, which gives police and healthcare authorities broader powers to deal with exceptional situations. Plan Blanc was last activated following the attacks in Paris in November.
Nice-Matin reported taxis were evacuating people from Promenade des Anglais free of charge. About 100 people fled out to sea during the attack, but have now been recovered, Le Figaro reported.
The crowd had gathered at the Place Massena, the city's main square, and fireworks marking Bastille Day, a public holiday in France, had just been let off when the attack happened at about 10pm local time. The square is now cordoned off.
"It is absolute chaos," said an eye witness who works in the Nice judiciary.
"There are reports of dozens of people killed, and many more injured. Bodies are lying everywhere.
"Police are flooding the streets, including anti-terrorism officers. Nobody knows what to do, except to hide away. Gunmen are meant to be targeting hotels."
Australian woman Sophie Sanderlands is on holiday in Nice, and has spoken to local breakfast show Sunrise.
"We were on the beach front enjoying the fireworks," she said.
After the display ended she and her friends starting walking towards where the attack occurred.
"There was live music, people everywhere, it was a really happy mood," she told Sunrise.
"All of a sudden thousands of people just started running towards us screaming, crying, absolutely out of control."
She said she had no choice but to run with them.
As they ran towards Place Massena there she saw strollers on the ground, and people desperately trying to get inside packed restaurants.
Iranian journalist Maryam Violet, on holiday in Nice, told the Guardian she saw the truck run over people as they walked in the pedestrian area after fireworks had finished, and described seeing "dead bodies all over the place".
"Everyone was completely shocked, I saw that suddenly people were fleeing and shouting," Violet told the Guardian.
"People were shouting 'It's a terrorist attack, it's a terrorist attack', it was clear that the driver was doing it deliberately.
"I was walking for nearly a mile and there were dead bodies over the place. I think over 30 dead bodies are on the ground and lots of people are injured."
The area around the Promenade is full of hotels and restaurants, which were all packed for the national holiday.
Prime Minister John Key watched the attacks on TV in Paris, where he and his family attended Bastille Day celebrations with French President Francois Hollande.
US Secretary of State John Kerry was also at the event, held under tight security because of terrorist attacks in Paris last year.
Key, his wife Bronagh and children Stephanie and Max watched the military parade along the Champs Elysee. to mark the start of the French Revolution - the storming of the Bastille.
He posted a tweet saying his thoughts were with the victims.
A Ministry of Foreign Affairs and Trade spokesman said 882 New Zealanders are registered as being in France.
"The Ministry of Foreign Affairs and Trade is aware of the incident where truck crashed into a large crowd attending a Bastille Day event in Nice, France.
"The New Zealand Embassy in Paris is liaising with the local authorities to ascertain whether any New Zealanders have been harmed."
The Guardian reported jihadist propaganda had suggested using a vehicle ploughing into a crowd as a terror attack for several years.
Facebook has enabled safety check so people in the area can notify friends that they are okay.
Hollande also extended by three months a state of emergency that was supposed to have ended on July 26.
"Nothing will lead us to give in to our will to fight against terrorism. We are going to strengthen our efforts in Syria and Iraq against those who are attacking us on our very soil."
He said he would go to Nice on Friday (French time) to support the city.
MFat's Safe Travel website advises New Zealanders to stay away from the area, and follow the instructions of authorities.
• Contact your family in New Zealand to advise them that you are safe
• New Zealanders who require consular assistance are advised to contact the New Zealand Embassy in Paris on 01 45 01 43 43.
• If you have concerns about a New Zealand citizen family member in France, please try and make direct contact in the first instance.
• If you have ongoing concerns, please contact the Ministry of Foreign Affairs and Trade on 04 439 8000 (if calling from within New Zealand) or +64 4 439 8000 (if calling from outside New Zealand).
• Please pass this message to any New Zealanders you know of in Nice who may not have registered their details with us.