Crews were called to Wicksteed Leisure in Digby Street last night by workers who smelled the smoke and feared their factory was alight.

When firefighters arrived they found the roof of another building, in neighbouring Lawson Street, ablaze and smoke pouring from its roof. The blaze engulfed the Whitfield Wiley building which is partially occupied and one onlooker said he had seen the smoke from Bath Road.

Resident Steven Baynes, of Digby Street, said: "The whole street was full of smoke, it was like a fog."

"I could smell the smoke and heard the fire engines about 10 minutes later.

"They blocked the road off a while after the first fire engine arrived. I thought the fire was at Wicksteed Leisure."

Wicksteed Leisure worker Andrew Nicol, from Kettering, raised the alarm and rang the fire brigade. He said: "We smelled the smoke and thought our building was on fire. It was about 7.15pm and there were only two of us working. It was a bad fire."

Watch manager Thom Stitt at county fire control, said crews were called out just after 7pm.

Four pumps, an ariel ladder platform and a support pump from Rothwell, Burton Latimer, Wellingborough, Thrapston and Moulton stations were at the scene of the fire.

Mr Stitt said: "The property is believed to be the former Whitfield Wiley building.

"It has two floors and is partially occupied."

He said the blaze had been confined to the first floor and the roof of the building.

The fire service said last night the cause of the blaze was not yet known but investigations would be carried out.