AN ARSON probe has been launched after a major fire caused rush-hour chaos across Southampton.

A blaze broke out above Paddy Power betting shop in Shirley High Street on Wednesday morning, resulting in police closing the road.

It caused gridlock for motorists, who were already facing lengthy delays due to work on the nearby Millbrook roundabout.

Hampshire Constabulary confirmed it was now treating the incident as arson and is urging anyone with information to contact them.

More than 30 firefighters from across Hampshire tackled the fire, which took seven hours to fully extinguish.

The Shirley area has seen a big increase in commuter traffic since work on the roundabout started several weeks ago.

A large number of motorists heading into Southampton are using the High Street to bypass the area or avoid the long tailbacks which build up on the M271 and the A33 Redbridge Road.

But part of the High Street was closed to traffic for almost four hours as firefighters fought the flames.

The blaze broke out shortly after 5am, engulfing an empty flat above the Paddy Power betting shop and destroying the roof.

Workmen said their site office was in the Paddy Power building until last week, when it moved to one of the flats under construction. However, paperwork which had yet to be transferred is thought to have been lost in the blaze.

One woman said: "The flames were quite high and four or five firefighters with hoses were blasting them with water. It was quite scary."

Paddy Power, a former pub, is at the junction of High Street and Crown Street.

The front of the property was covered in scaffolding and locals said it was either being rebuilt or refurbished. The fire appears to have started on the first floor before spreading to the roof, which later collapsed.