Several hundred people in New Zealand have been evacuated from their homes with some recounting dramatic helicopter rescues after heavy rain caused widespread flooding in the Canterbury region.

Authorities declared a state of emergency after some places received as much as 40cm of rain over the weekend and into Monday.

Forecasters warned of possible heavy rain through Monday evening before conditions improved.

The military helped evacuate more than 50 people including several overnight in an NH-90 helicopter.

One man was clinging to a tree near the town of Darfield when he jumped into floodwaters and tried to swim to safety but was swept away, the military said.

Helicopter crews scoured the water for 30 minutes before finding the man and plucking him to safety. The military helicopter also rescued an elderly couple from the roof of their car.

“Seeing the community overnight pull together and support the displaced residents who were evacuated from their homes has been heartening,” said Army Liaison Officer Captain Jake Faber.

Another man was rescued by a civilian helicopter pilot on Sunday after he was swept from his farm as he tried to move his stock to safety.

Paul Adams told news organisation Stuff he thinks he got hit by a wall of water he didn’t see coming.

He was swept down the raging Ashburton River before managing to drag himself onto a fence and then into a tree. Another farmer spotted his headlamp and organised a rescue mission.

“The rescuers are fantastic,” Adams told Stuff, adding that he was now back on his farm and “good as gold.” He said that so far he’d only found about 100 of his herd of 250 animals alive.

Australian Prime Minister Scott Morrison, who was visiting New Zealand, told reporters that he was thinking of those caught up in the floods.

“Australia is no stranger to floods,” Mr Morrison said.

“Or fires, or cyclones, or, indeed, even mouse plagues. We have, both countries, endured a large amount of challenge over the course, particularly, of these last few years.”

New Zealand Prime Minister Jacinda Ardern planned to travel to Christchurch later on Monday to be briefed on the situation firsthand.

-AAP