A blaze in an abandoned building in central Wellington is being investigated as suspected arson.

The fire at the old Boys’ Institute on Tasman St in Mount Cook has been extinguished, but the building has been “virtually gutted”.

Firefighters risked their safety to search the interior of the building, despite fears it could collapse, as they were concerned squatters could be inside - but nobody was found.

The fire is being treated as suspicious, and police and Fire and Emergency New Zealand (Fenz) are investigating.

Emergency Services on the scene of a fire at the Old Wellington Boys’ Institute on Tasman St. The derelict building is owned by the Chinese Government. Photo / Ethan Manera

The blaze was first reported at 12.23am. The building was “well alight” on arrival, and a second alarm was raised, Fenz central shift manager Murray Dunbar said.

Crews from Newtown, Brooklyn, Wellington City, Kilbirnie, Thorndon, Remutaka and Karori responded.

Dunbar the building, which is made of brick and concrete or stone, had been abandoned for some time and was significantly damaged.

“It’s virtually gutted inside. There are fears that the integrity of the building has been compromised,” he said.

There was a fire at the derelict Old Wellington Boys’ Institute on Tasman St this morning. Photo / Ethan Manera

“Because it was abandoned and the state of it, and fears of potential collapse, most of the firefighting was external.

“However, crews did conduct an internal search because there were fears in the early stages that there may have been squatters in there, but that subsequently proved not to be the case.”

Firefighters will likely remain on standby for much of the day.