Horrifying pictures of the Nepal flash flood are being described as "like watching a dramatic movie" by a New Zealand-based Nepali man.

Five New Zealanders are among more than 1000 people missing following Wednesday's catastrophic flash flooding on the Nepal-China border which has killed hundreds.

Rescuers continue to search the Himalayan valleys and hillsides after a flood that has killed at least 359 people, Reuters reports, as Nepal and China warned of a risk of fresh flooding from water pooling in two lakes.

Both countries say a glacier collapse on Wednesday morning sent a huge torrent of rock, ice, mud and debris cascading through Himalayan mountain river systems, sweeping through villages and key infrastructure down a route thronged by trekkers and pilgrims that links Kathmandu with Lhasa in Tibet. Of those missing, at least 540 are foreigners.

Suhasini Reddy is one of five New Zealanders missing in Nepal. Photo: supplied

RNZ understands four of the five New Zealanders missing are Suhasini Reddy, who lives in Australia, Auckland man Dejan Kuzmic and Hamilton couple Mihir and Kinnari Patel.

The identity of the fifth person has not yet been confirmed.

Based in the Canterbury town of Lincoln, Dr Sulav Paudel said seeing the disaster unfold was unlike anything he had seen.

"It's horrifying. It's like things we see in dramatic movies. Most of us haven't slept well."

Dr Paudel is the treasurer for the New Zealand chapter of the Non-Resident Nepali Association (NRNA).

The group had issued an urgent plea for donations as it tries to raise emergency relief funding for the Nepal government.

NRNA New Zealand was working with other NRNA groups within its international network, including a team on the ground in Nepal.

Its executive team met on Thursday to discuss how New Zealand-based group could respond to the disaster.

Dr Paudel said it had reached out to the Ministry of Foreign Affairs and Trade to advocate for support from the New Zealand government for the disaster recovery.

He hoped the government would soon formally acknowledge the event, including what support it might be able to offer.

"In the meantime we're also looking after our members to see whether there are any families or people who have loved ones that need support.”

Given the event was still unfolding, Dr Paudel said it was too early to determine to what extent New Zealand-based Nepali may have been personally affected.

"There are so many people that are out of reach that we don't know what has happened to them yet.

"In terms of actual casualties, I don't think we've heard from anyone. We expect the number (of casualties) to go up."

There were about 1350 members of NRNA New Zealand.

A candlelight vigil for the victims of the Nepal disaster was due to be held in Auckland's Aotea Square on Saturday.