A mysterious explosion near the Manawatu River has baffled residents and authorities in Palmerston North.

Hokowhitu residents around Heatley Ave and Hind Place reported a loud bang, orange light and smoke near the river about 10.30pm, on Wednesday.

Heatley Ave woman Helen Hughes was in her office, which faces the river, when she heard the explosion.

"It was extraordinarily loud because everybody thought it was in their backyard ... I thought it had shaken the house."

"I saw the light that accompanied the noise and it was orange and at sky level."

Mrs Hughes said a lot of people came outside to investigate.

"One said they saw smoke in the direction of the river. Another said they saw a blue light in the direction of Crewe Cres."

A possible cause was someone blowing up a gas canister but a scan of the riverbank by a Manawatu Standard reporter and photographer revealed no scorch marks or debris.

Another Heatley Ave resident who heard the bang was Tatyana Pinkney.

"It was really weird, and very loud ... it sounded like a gunshot."

It was a still night so Mrs Pinkney listened out for footsteps or talking after the bang, but heard nothing.

Authorities have been unable to explain what caused the explosion.

Police investigated after receiving a call from a Hind Place resident, but did not discover the origin of the blast.

Metservice spokesman Bob McDavitt said it could not have been a lightning strike because the nearest thunderstorm was in Waikato.

Palmerston North Airport chief executive Garry Goodman said he was unaware of any activity in the air space.

Linton Army Base spokesman Paul Stein said there was no live firing in the area at the time.

Do you know what caused the explosion? Write to the editor at PO Box 3, Palmerston North, or editor@msl.co.nz (include names and addresses), or text 0274981242.