Emergency workers at the scene of a fatal plane crash in Raglan have retrieved two bodies but the mangled wreckage is about to be swamped by the incoming tide.

Two people died after a light plane crashed onto mudflats on the outskirts of Raglan this afternoon.

Emergency services were called to the incident shortly after 3.20pm following reports the aircraft had crashed into the harbour.

Police said in a statement around 4.30pm it was understood two people had died but medical staff at the scene were yet to confirm this.

No other people were in the plane and no injuries had been recorded on the ground, police said.

A Herald reporter at the scene confirmed two bodies were retrieved just before 6pm. The incoming tide had now surrounded the plane. The wreck would have to remain in situ overnight.

Earlier, firefighters carried stretchers to the crash site before removing the bodies. The stretchers were also used to transport parts of the aircraft's wreckage back up to a nearby embankment for investigators to examine.

Prior to being completely surrounded by water, forensic staff had to stand on the wings of the plane to examine the wreck.

Several firefighters were now combing the wetland and surrounding grassy area for evidence linked to the crash.

Raglan resident Thomas Malpass said he witnessed the aftermath of the crash.

"It is a pretty grim scene. Some citizens were first on the scene, they managed to get across the farmland, but there was not much they could do. The people in there were obviously deceased."

Malpass said the plane had crashed into mudflats in the Kaitoke Harbour.

"You can't see many tyre tracks, I wonder if they planned to land it. The plane looks like it might be half, one of the wings is off."

A group of trainee pilots saw the plane performing a manoeuvre from the sky before they lost sight of it.

They thought it was a strange manoeuvre to perform at the low altitude it was flying.

They said they didn't see it crash and weren't sure what had happened but believed it had somehow lost control.

The group told the Herald they were trainee pilots and the crash had freaked them out "a bit".

A neighbour said she heard an "almighty crash" before seeing the plane crashed on the mudflats.

A Herald reporter at the scene said the wreckage was covered by a tarpaulin and appeared to have crashed at low tide.

She was told by a local who originally thought there was a car crash, his neighbour alerting him to the plane crash.

Together the two local men raced over to the crash to see if they could help but the two occupants had already died.

One of the men said he was unable to describe what sort of plane it was and said it was a "mangled wreck".

He said it was common to hear planes overhead as it was on a route to the local airport.

Robertson St resident Joy Utting said she was folding washing in her bedroom, overlooking the Kaitoke Estuary, when she heard a hissing noise.

"It sounded like a gas canister, it must have been from the impact hitting the ground."

She said she ran outside, looking up and down the street before spying the wreckage across from her property.

"There were these people running over to help ... but their body language told what was happening straight away, that it wasn't good."

Another Raglan local described hearing "a big bang" and assumed it came from a nearby car crash.

The woman could not see the crash from her property but told the Herald she got a fright from the loud bang.

"I heard a big bang and I got such a fright. I wondered it what it was. It was very scary," she said.

"I didn't know it was a plane, it was so quick."

The woman felt guilty for not going to help but said she didn't realise it had crashed into the adjacent estuary.

"I saw a car there earlier on the farm but then I suddenly saw an ambulance thought it was that."

A Fire and Emergency New Zealand spokesman told the Herald earlier that one appliance from Raglan was attending.

He said the crew accessed the aircraft on foot but couldn't confirm if the plane had crashed into the water or dry land.

Initially, emergency services attended the incident from East St but said access was easier from a property on Main Rd, the Fenz spokesman said.

Fenz crew said earlier they would not be extricating the occupants of the aircraft until police had made their inquiries.

St John spokeswoman Ngaire Jones told the Herald an ambulance was still on scene but any information would have to come from the police.

Police said the Civil Aviation Authority had been notified about the fatal crash.

In 2016, a pilot escaped with minor injuries after a light plane crashed at the Raglan Airfield.

The aircraft crashed on landing and went through a fence, suffering "material damage".

And another light plane crashed into the water and sunk off Raglan Beach on Boxing Day 2014.

That incident, involving a Piper Cherokee, happened 100m off the beach which was packed with holidaymakers.

Police said it appeared the plane's engine cut out just after take-off and the pilot was attempting to make it back to the airstrip.

Three people onboard the aircraft were injured during the incident.