POLICE were last night investigating a major warehouse blaze in the heart of a busy shopping area.

More than 40 firefighters tackled the blaze yesterday afternoon at Portrack Workshops, on the North Tees Industrial Estate at Stockton.

Thick black smoke, which billowed 150ft into the air, could be seen several miles away.

A spokesman for Cleveland Police said that the blaze was being treated as suspicious and appealed for any witnesses to come forward.

The building houses two firms, Ultralux and Florist Supply and Display.

The area, which was busy with shoppers, was closed to the public while firefighters fought to keep the flames under control.

At the height of the blaze, there were seven fire engines, two hydraulic platforms, two emergency tenders and about ten police vehicles.

District manager at Stockton fire station, Phil Lancaster, said that initially, three fire crews were sent, but realising it was a massive blaze, called for back-up.

"We are not sure what happened," he said. "Fortunately there was no wind and that really helped us as the smoke just went straight up, otherwise we may have had to shut the A19 to as far back as the A174."

Witnesses said they believed the area was used for illegal fly-tipping and this may have been partly to blame for the fire. But Mr Lancaster said: "I have not been made aware of any fly-tipping, and we are carrying out investigations to determine the cause of the blaze."

Malcolm Bendelow, who works nearby, was one of those to first see the smoke.

He said: "I saw small wisps of smoke come from the building and from behind it, and then the next thing I knew there must have been a rush of oxygen and the smoke just went up like a rocket."

Anyone with information about the fire is asked to call Cleveland Police on (01642) 326326.