Hundreds of people have had to leave their homes as parts of New Zealand are hit with what has been described as a one-in-100-year deluge.

Worst-hit was the province of Canterbury in the country’s South Island, where at least 300 homes had to be evacuated overnight.

Several roads, schools and offices were closed.

A state of emergency was declared in the region following similar declarations on Sunday in the nearby areas of Timaru, Selwyn, and Ashburton.

In Ashburton, about 50 miles southwest of Christchurch, 19 roads were closed and three bridges had collapsed or been washed away, according to NZ news website Stuff.

The town’s mayor Neil Brown said on Facebook that the river was running at 1400 cumecs (cubic metres per second) instead of its usual 10 cumecs.

He told the NZ Herald that “half of Ashburton” would need to be evacuated if the river’s levees broke but there was “still quite a bit of capacity”.

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“We really need it to stop raining to let those rivers drop,” he added.

The New Zealand Defence Force used helicopters to rescue three people stranded in flooding in the surrounding area.

The Royal NZ Air Force said the crew of one of its NH90 helicopters had rescued a man from a tree surrounded by floodwater in Darfield and an elderly couple from a car roof in the small town of Ashburton Forks.

In Akaroa, a small town about 50 miles southeast of Christchurch, Christchurch City Council said flooding appeared to be caused by blocked pipes.

Residents were warned the water could be contaminated and they should take precautions such as changing out of wet clothing and washing their hands as soon as possible.

A number of surrounding roads have been closed due to slips.

Further south, Environment Southland activated its flood warning system as persistent rain caused river to rise.

The country’s MetService issued warnings for heavy rain in Canterbury and elsewhere until later on Monday morning UK time.

It said that the main focus would be north of the Rakaia River in the Canterbury Plains, where 50-90mm could accumulate, on top of the rain that has already fallen during this event – more than 400mm in some parts.

The government announced a NZ$100,000 (£51,000) fund to support Canterbury people affected by the floods.

New Zealand’s acting minister for emergency management Kris Faafoi said: “While it is still very early to know the full cost of the damage, we expect it to be significant and this initial contribution will help those communities to start to get back on their feet.”