A Hastings helicopter pilot has described the mad dash to rescue people trapped on roofs across the Hawke's Bay as Cyclone Gabrielle caused rivers to burst, completely submerging some homes.

Rotorforce Helicopters boss and chief pilot Joe Faram said about a dozen helicopters from the Defence Force, rescue services and private operators plucked up to 400 people to safety.

Some were in poor condition.

"There was one very trying situation I was involved in where an elderly lady was stuck up a tree and her husband was on the roof, and by the time we managed to extract them, I had to fly them directly to hospital, because she was quite hypothermic and very weak.

"I also had one case where I flew a man off a roof and he had his leg in plaster and a whole lot of young children and I flew a young couple off with a new-born."

The small township of Fernhill west of Hastings after the Ngaruroro River burst its banks. Photo Supplied - Dawson Bliss

Faram also flew during Cyclone Bola in Gisborne and said the devastation this time was just as bad.

"It's more localised. There's some severe flooding with homes that are completely under. All day today [Tuesday] I've been evacuating people from the roofs of their homes, and when we first started, the water was about a foot under the eaves and by the end, the water was over the very top of the houses."

He made rescues in Puketapu, Waipawa and around Hastings and Napier.

"This is serious devastation; bridges are washed out, there's no power, no cellphone coverage. So we're just flying around [seeing] people on homes and on their roofs and having to fly in there and pick them up evacuate them and some cases animals as well."

Faram said flying conditions were difficult.

"Initially, it was windy and then wind dropped quite a bit, but it was raining and drizzling on and off all day, so it was poor visibility, very limited visibility, very much a rescue situation for flying, yeah."

And extracting people was nothing short of unbelievable.

"Very tricky flying, landing on the roofs with the helicopter. The Air Force was here - they did some winching. The local rescue helicopter did some winching on the roofs we couldn't land on because of trees or power lines," Faram said.

The recovery from the flooding would be difficult for many of those rescued, he said.

"There's going to be a lot of homeless people and a lot of homes destroyed. I just couldn't believe the water level wasn't just up to the door step - it was going over the top of the roof right on the edges of the city which is quite unbelievable.

"So, there's going to be a lot of people who've lost 100 percent of their belongings and their homes."