The fire at Bank Bottom Mills in Marsden is being treated as suspicious.

Huddersfield watch commander Andy Wooler from Huddersfield Fire Station said crews could not explain why the fire started where it did - meaning the circumstances are suspicious.

He said material trapped in the void between one of the mill floors and the ceiling below had caught fire, filling the mill with smoke.

Firefighters spent six hours tackling the blaze.

Mr Wooler said: “It is a huge mill so there was a possibility of the fire spreading and the whole mill going up.

“One floor was fully smoke logged.”

Fire, Bank Bottom Mills, Marsden. Fire crews wearing particle masks deal with the fire in the centre of the mill complex

He said firefighters equipped with breathing apparatus had to work in thick smoke and dangerous conditions.

“We are very cautious. Trying to find your way through and not knowing where the fire is - that’s what kills firefighters,” he said.

Live: "Substantial" fire at derelict mill in Bank Bottom, Marsden

Because more breathing apparatus and oxygen was needed, at 1.30pm the officer in charge called for a further six pumps (fire engines).

Mr Wooler said: “The fire started in a wooden floor - there is a 12” gap between the floor and the ceiling.

“Over the years, when the building was a textile mill, lots of dust and cotton fell into the void. All that was on fire.

“The firefighters were working with this and it could have collapsed at any time.

“This was why it took so long.”

Fire, Bank Bottom Mills, Marsden. Emergency services at the fire at Crowther's Bank Bottom Mills

“We didn’t identify the fire until two hours into the job because the building was smoke logged.

“An area about 20m by 30m was on fire.

“There was nobody inside so we didn’t have to go looking for anybody - we just couldn’t find the site of the fire.”

“Once we started peeling up the floor we had access to the dust and materials that had been smouldering for a few hours.

“Looking at where and why it started, a fire shouldn’t have started there so we believe it is suspicious.”

The fire started at about 1pm and fire, police and ambulance crews attended.

Ambulances and the fire service's personnel welfare unit were in attendance for the crews working on the fire in case there was asbestos in the building.