The two men who died in a plane crash at Raglan yesterday were believed to be visiting the seaside town during a test flight.

The Herald understands the owner was currently in the process of selling his Vans-RV4 light aircraft and was taking a prospective new owner on a quick trial flight.

The bright yellow plane is based in Auckland while it's believed the owner got his father to carry out the test flight for him. The owner's father, who died, lives in the Marlborough region.

Emergency services arrive at the scene where a light aircraft lies crashed on the mudflats at Raglan. Photo / Belinda Feek

It is not known who was flying the plane when it crashed.

A source told the Herald it's not uncommon for pilots to take the quick 30 minute trip down to Raglan either as a social visit or to show off the qualities of a plane.

"Raglan's a very popular place to fly to. You can land and walk across the bridge to the shops and cafes. It's a safe, short, trial flight, it's only 30 minutes."

According to CAA information, the victim's son has owned the plane since June last year and been flying for about two years.

Police said they were now investigating on behalf of the coroner. They did not expect to release the men's names until late today or tomorrow.

Meanwhile, Civil Aviation Authority investigators have arrived at the scene of the crash.

Emergency services raced to the scene, in the mudflats of the Kaitoke Estuary, opposite Robertson St, about 3.20pm yesterday.

Neighbours who saw the plane plunge from the sky also ran over to help the two occupants only to discover they did not survive.

The Disaster Victim Investigation team, along with other emergency service crews, were then left racing against time due to the incoming tide.

The plane the pair were flying in was a Vans-RV4, one of the most popular light aircraft in America, Australia and other parts of the world, an industry insider says.

He had seen the plane in Waharoa before but had not seen it for a few months.

Western Waikato police area Inspector Andrew Mortimore said they ended being "reasonably lucky" in getting the two occupants out before the plane was surrounded by water.

The tide wasn't as deep as they expected though, less than the approximate 30cm to 60cm.

The wreckage of a light aircraft, a yellow Vans RV-4, lies embedded in the mudflats of the Kaitoke Estuary after crashing about 3.20pm on Monday.

Crews also picked up vital evidence for both CAA and forensic staff who would try a build a picture of how fast the plane was going before it slammed into the soft terrain.

Mortimore confirmed part of the plane was embedded in the mud on impact.

It was then secured by firefighters who used a rope to ensure it didn't move overnight.

Mortimore said they were still working on the occupant's identification and liaising with next of kin. He would not be drawn on the gender of the deceased or where they were from.

Residents and witnesses yesterday recalled seeing the plane performing a "strange manoeuvre" before careering to the ground.

A group of trainee pilots saw the plane performing an aerial manoeuvre before they lost sight of it.

They thought it the plane was flying "pretty low for what it was doing".

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

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

Another neighbour said he heard what he thought first was a car crash, before his neighbour alerted him to the downed plane.

Together the man and woman raced over to the crash to see if they could help but the two occupants had already died.

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."