Police were still trying to establish how the man came off the bike. Mr Scarrow said the man was not wearing a helmet.
"We have spoken to witnesses and we will speak to more."
Unlawful use of similar vehicles in the area was common, he said.
"Over the years, because it's a beach suburb, we often get reports and see ... trail bikes and other bikes riding in the area to and from the beach.
"From time to time, there is excessive speed and no helmets being worn, which concerns us greatly."
The man lived in the area and police were speaking to his family.
Hood St resident Hannah Taylor said she came out of her house when she heard sirens and saw a group of six people around the man.
Four of the men "took off" when they heard the sirens, she said. "One guy was like, 'Nah, he's gone' - that's when they ran off."
One of the men drove past the crash site later in the day, Ms Taylor said.
The remaining two men stayed, and Ms Taylor later saw them leave in a police car.
Mr Scarrow said the men were believed to have been family members of the man who died.
"I don't think there was anything suspicious - it was just a reaction by them at the time."
Another resident said people on quad bikes and scooters were always "hooning up and down the street".
Police are seeking witnesses and anyone with information should call Constable John Redley at the Wanganui police station on 06 3490600.
