More than a dozen students were injured at a Dunedin party when a balcony collapsed during a concert by the band Six60.

Police were called to an address on Castle St tonight and were working to clear the confined area when the accident happened.

Up to 1500 students were at the Dunedin party.

"Police and Campus Watch [staff] were attempting to clear people from the rooves and reduce the number of people on balconies when one of the balconies collapsed - throwing people to the ground approximately 3m and collapsed decking landing on people in the courtyard area,'' police said.

Fourteen people have been injured, eight badly, after a balcony collapsed in Dunedin during a concert by the band Six60. Video / James Gunn

A total of 17 people have tonight been treated at Dunedin Hospital. Two of those people are said to have suffered serious but non-life threatening injuries. The remaining 12 suffered "less serious'' injuries.

Police officers will remain at the site overnight.

Witnesses have described seeing bloodied, injured people - described by police as "walking wounded" - after the incident this evening.

Students had packed surrounding balconies as the band played near their old flat at 598 Castle St.

The band continued playing after the collapse, and people remained on adjoining balconies.

A St John ambulance spokesman said four ambulances and a rapid response were sent to the scene the scene.

A neighbour of the house where the balcony collapsed said there were too many people jumping on the structure - which was bolted to the house with no support beneath.

"I heard a giant crash. I looked out and people were on the ground. Legs were broken. There was shock and hysteria - a lot of people were drunk.

"People were walking down the street covered in blood. There were big manly guys in tears. We were trying to comfort people and give them water - everyone was in shock"

Despite the collapse, people on other balconies at identical units continued jumping, while others remained beneath the structures. She said more people flocked to the party, to see what the commotion was about.

It was part of the mentality among students in Dunedin, she said - when something happened, everyone flocked to check it out.

"Fire crews had to come in and ask them to move."

She said there weren't many people on the balcony at the time, but they were not strong.

After the accident, people continued to party.

The band responded on Twitter tonight.

"Very upset that people were hurt tonight. Massive thanks to the local police and security who were working with us to help keep people safe."

A fifth year student who was at the concert described the moment the balcony came down.

"There was probably 15-20 people up there on the balcony. They were just having a good time and all of a sudden it collapsed," he said.

"It landed on about 10 to 12 people."

The student said he looked on in horror as the balcony came down.

"It was like a big crack and then everyone winced ... when you see something like that ... It's one of those things that you never want to see."

Emergency services attend the incident on Castle St. Photo / Rhys Chamberlain
Emergency services attend the incident on Castle St. Photo / Rhys Chamberlain

He said the crowd's actions in the aftermath of the collapse were admirable.

"The students were helping the ambulance staff. There were a couple of cars in the way and 15-20 guys just lifted the cars, moved them out of the way so the ambulance could get in," he said.

"It was horrific ... there were unconscious people under the balcony ... I saw limbs underneath. But out of respect to them I won't say anymore. It is not something you want to be picturing."

After the balcony came down the band kept playing.

"It happened on the far left [of where they were playing]," he said.

"They didn't realise. As soon as they did realise they cut the music and everyone was out of there."

Jessica Douglas-Withers, a medical student at Otago University, was at the gig. She said suddenly there was a big creak.

Emergency services attend to people who fell from a collapsed balcony at a Six60 concert in Castle St, Dunedin. Photo / James Gunn
Emergency services attend to people who fell from a collapsed balcony at a Six60 concert in Castle St, Dunedin. Photo / James Gunn

Everyone turned around and watched the balcony fall off the side of the building, she said.

As she left she saw three injured people lying on the ground.

Another eyewitness told the Herald he saw people leaving the address bleeding from the head and feet.

He said the event was held at 598 Castle St. Up until this year the band held the gig at their old flat, 660 Castle St, but due to limited space they moved it tonight.

"We were there earlier and it was all pretty good, people were having a good time," he said.

"I looked at the balconies and I thought to myself 'if they fill up too much they might collapse as a consequence'."

A witness said some people continued to party afterwards.

"Police tried to break down a fence to make way emergency services."

Some people were in shock, some had broken limbs, she said.

A witness said the band continued playing after the balcony collapsed.

The scene at Castle St Dunedin after a balcony collapsed during a Six60 concert. Photo / Otago Daily Times
The scene at Castle St Dunedin after a balcony collapsed during a Six60 concert. Photo / Otago Daily Times

No commotion could be heard from the stage, and it was only later the band realised what had happened.

About 300 to 400 people were at the concert, the witness said.

One lane is closed on Cumberland St, with emergency services gathering by the Dundas Corner Dairy.

A dairy worker said students had been coming in talking about the incident.

Shopkeeper Jenny Shen said: "Some students came in and said there were many students injured. They saw blood on their faces and it was very serious."

Ms Shen said she could still see three ambulance vehicles, fire trucks and dozens of police officers next to her shop.

"It's still very noisy and there's still some students dancing on the roof. Police are telling them to come down."

Otago University's vice chancellor, Professor Harlene Hayne, said they were offering full support to those students injured tonight.

"Our thoughts and deepest concerns are with the students, their families and friends at this time.''

She said staff were not aware of the concert until late this afternoon.

As a result, the university's own security staff - Campus Watch - went along to the concert and police were also notified.

"Fortunately [they] were present to help out with first aid to the injured immediately after the balcony collapsed.''

Last week police arrested up to 13 people in Dunedin when student parties got out of control.

According to the Dunedin Flat Names website, members of Six60 had moved into the Castle St house with friends from university.

"They had spent time jamming in their rooms and thought it'd be good to flat together and get a band going," the site said.

"They referred to the flat amongst themselves, and to others, as 660, and as the band formed and they started playing shows, they became known as the 660 boys. When it came to releasing their first EP, they decided to call themselves Six60, after that Castle Street flat because 'it was a place that meant so much to us'."