Hundreds of people have been evacuated in New Zealand as floods swept through southern parts of the country following heavy rainfall.

Authorities told residents to “not be complacent” and advised them to leave their homes immediately in low-lying areas of Southland due to rising river levels.

Nearly two hundred tourists were also rescued – many by helicopter – from the picturesque fjord of Milford Sound after floods and mudslides swamped roads on the natural attraction.

A state of emergency was declared in Southland, where people in the towns of Gore, Mataura and Wyndham were told to leave their properties early Wednesday morning (local time).

Emergency Management Southland urged people to “go and stay with friends and family on higher ground if possible” or to gather in certain community spaces.

Hamish Walker, the local MP, said authorities warned him they were dealing with a “one in a 100 year flood”.

Aerial footage showed water covering roads and fields, while a high river can be seen rushing past nearby buildings in another video.

Speaking on Wednesday, Mr Walker says: “It is quite strange. It is actually quite a sunny day.”

Further rainfall is forecast over the coming days, but not the heavy rain that has caused the flooding.

Authorities told Gore residents on Wednesday evening that they could go back to their properties as the Mataura River had gone down after it peaked around midday.

Emergency Management Southland said other evacuated locals would have to wait until Thursday morning to know whether it is safe for them to return home.