The pilot of a helicopter that crashed into Pauatahanui Inlet near Porirua says he is lucky to be alive.

Police, fire, ambulance, and the coastguard responded after they were alerted to the crash this morning.

The pilot, Rick Lucas, was the only person on board and was assisted out of the water by two bystanders who paddled out to him on kayaks after the crash.

Mr Lucas said he is uninjured apart from a few sores.

He said the helicopter started to go down after an intense vibration that continued to get louder.

"I had a tail rudder failure of some sorts.

"I felt quite an intense vibration that got worse and worse and the machine started to rotate.

"I just carried out what are considered to be the normal emergency procedures and got away with it."

Photo: RNZ / Rebekah Parsons-King

Mr Lucas said he was submerged in water but managed to free himself to climb on top of the helicopter to wave for help.

"I didn't panic. I almost went into some sort of state that allows you to think logically and consciously.

"I looked for the seatbelt, found it and released it. I thought my leg was trapped, it was my biggest concern."

He described the experience of going down as "frightening".

"I wasn't feeling happy.

"I think for the first time ever in a helicopter, I thought this is it. Going in the water was the biggest concern. Going in the water and being trapped.

"I had a good outcome."

Adam Power was nearby and kayaked out to Rick Lucas to help him.

"Me and a friend were just mowing a lawn ... literally across the road.

"The chopper went down behind us, we heard a commotion, turned round and the chopper was in the water on its side.

"We could see a guy climbing out and standing on top of the roof. I saw a kayak next door to the house we were mowing so I pinched it and went out to him."

Photo: RNZ / Rebekah Pasons-King

Maritime New Zealand's rescue coordination centre has been set up, and was working with the Civil Aviation Authority, the Transport Accident Investigation Commission and the harbour master.