More than 3.5 million people are estimated to have been affected by the devastating earthquake which hit Nepal on Saturday, with thousands in desperate need of urgent help, Oxfam says.
The international aid agency is preparing to bring clean water, toilets and shelter to the area, with its initial effort aimed at reaching 350,000 people.
Working across four open air sites in the Kathmandu Valley, the charity has been delivering water and building toilets.
"Over the coming days we will work with other agencies to provide clean water to 16 open air sites set up by the government of Nepal and to provide food and shelter, while also expanding operations outside Kathmandu," Oxfam said.
It has so far raised more than $1.5 million globally, but says more is needed.
"The generosity of the public has been overwhelming and timely. However, as millions are now without safe shelter, clean water and sanitation due to this tragedy, more is needed," Oxfam New Zealand's executive director, Rachael Le Mesurier, said.
More than 3.5 million people are estimated to have been affected by the 7.9 magnitude earthquake that struck on Saturday. The death toll currently stands at more than 4000, and is continuing to rise as reports filter in from harder to reach areas.
"Nepal is among the world's poorest countries and lacks the infrastructure and resources to deal with a crisis of this scale. The world pulled together to support Christchurch, and we know Kiwis will do the same for our neighbours in Nepal," Ms Le Mesurier said.
"Our aim is to help as many people as quickly as possible through the money the public donates and through our determined team in Nepal.
"Hundreds of thousands of people have suddenly been left without adequate food, water, shelter and medical care. They are understandably desperate. We need to act fast."
More than 5 tons of water and sanitation materials have been sent from Oxfam's warehouse in Barcelona to help those hit by the crisis, the charity said.
A response team from India was sent to assess the humanitarian situation in Gorkha, the hardest hit district, while an assessment of what needs to be done to help people in Lalitpur, Lumjung District and across the border in India in Sitamarhi and Darbanga is also underway.
•To donate to Oxfam's humanitarian response in Nepal go to: www.oxfam.org.nz or phone 0800 600 700
Unicef targeting millions of children
Millions of vulnerable children are at risk following the earthquake, Unicef said as it prepared to deploy more staff and emergency supplies to the region.
The agency said it was aiming to reach almost 3 million children, out of an estimated 7 million population in 35 affected districts. It would focus on water and sanitation, nutrition, education and child protection.
"Even though it will be days or even weeks before we have the full picture, the vast scale of the devastation is already beginning to emerge," Unicef New Zealand executive director, Vivien Maidaborn, said.
"One thing we do know for sure is that the needs in Nepal will be enormous. Shelter is among the most pressing needs right now. People are sleeping outdoors as they're too afraid to be inside buildings for fear they will collapse around them.
"For children especially, this is in an incredibly traumatic time. The initial quake, the constant aftershocks and the sheer panic surrounding them are all too much for a child to have to process. And that's not to mention those that have been injured, separated from their families or indeed left orphaned."
Limited access to water, sanitation and hygiene facilities as well as medical treatment was also a worry, she said. The charity was delivering clean water and providing tents and supplies for temporary hospitals.
• To donate visit www.unicef.org.nz/nepal or text 'Nepal' to 2923 to make a $3 donation.