A MILL fire in Blackburn is being treated as arson.

The blaze at Slater's wood mill, Emerald Street, yesterday left a wall so unstable that four houses in the Brownhill area had to be evacuated.

John Taylor, a spokesman for Lancashire Fire and Rescue, said: "We are waiting for a full report, but firefighters found that a number of fires had been lit in different places within the building, which points to a deliberate attempt to set fire to the mill.

"Our crews concluded that the fire had been started deliberately."

Fire crews were forced to withdraw from fighting the flames after more than four hours as it was considered too dangerous to continue.

Sub officer Alan Burgess said: "The building is severely damaged and building inspectors must now decide whether it has to be pulled down."

A sniffer dog will now also be drafted in to help search for clues in the investigation.

Adam Scott, Blackburn with Darwen's director of housing, said: "The council's building inspector was called out by the fire brigade and took steps to ensure that there was no immediate danger from falling building masonry before the residents were allowed back in to their premises. He is working with the owner of the property to try and find a solution to the problems caused by the fire."

The mill was owned by Orion Industrial Units and had been leased to tenants for 12 months.