UPDATED 12:49PM More people are being evacuated near Tolaga Bay following torrential rain.

At least two families have been airlifted to safety already today.

Two adults and their four-year-old grandchild were rescued around 9am after spending more than four hours huddled on the roof of their home in the Mangatokerau Valley surrounded by a raging torrent.

Intensive care paramedic Shane Clapperton took part in the rescue and said the water was so powerful it swept a truck a kilometre downstream, and thousands of logs were strewn about.

The rescued family say they've lost everything, including their woolshed and a number of vehicles.

Eastland Community Trust Rescue Helicopter pilot Hamish Ramsay, who helped rescue the family, agreed the power of the water was immense. 

John Clarke from Tairawhiti Civil Defence says the family had been on the roof since 4am.

"The youngster was being assessed for possible hypothermia but otherwise they're fine.

"When you're wet and it's windy and you're on the roof, you're gonna get cold," he said.

Around 20 more people have been evacuated to Mangatuna Marae.

Gisborne Mayor Meng Foon says people near the Hikuwai River are also advised to evacuate.

Rivers in the area have risen rapidly since midnight.

Civil Defence said seven people may have been isolated in their home due to floodwaters, but they're not thought to be in any immediate danger.

Several roads in the area are also closed.

Metservice has now lifted their Heavy Rain Watch for Hawke's Bay, but periods of heavy rain are still predicted for the northern and eastern regions of the North Island and eastern Marlborough.

As well, there strong southerly gales forecast for eastern Otago, and significant snow for the south of the South Island.