RESCUE workers battled throughout the night in a desperate bid to save victims entombed in rubble after a factory explosion which killed at least four people.

Contact was established with five people trapped in the wreckage of the plastics factory in Glasgow.

And as the light faded, emergency services said they were unsure how many others may be buried.

The explosion destroyed Stockline Plastics, in the west end of Glasgow, shortly after midday.

Strathclyde firemaster Brian Sweeney said six casualties had been rescued from the collapsed building and his firefighters were in contact with a further five people buried beneath the rubble.

But he said: "We are unsure about precise numbers . . . we are in vocal contact with five people and I'm very optimistic those people will come out and be rescued in the next few hours, but the situation is changing from minute to minute."

Dozens of people were injured as the blast reduced the four-storey building in Grovepark Street, off Maryhill Road, to a pile of rubble in seconds, and covered cars and surrounding buildings in dust.

Scotland's First Minister Jack McConnell described the explosion as "tragic and terrible" and said his thoughts were with the family and friends of those involved.

Strathclyde Police said 40 people were confirmed as injured, of whom 16 were serious. They were being treated at five city hospitals.

Mr Sweeney likened the site to an earthquake scene and said the rescue operation, which was being treated as a major incident, could take as long as 48 hours.

Up to 200 firefighters were involved in the rescue and a number were among the injured.

The cause of the blast was still being investigated, although survivors suggested four ovens in the factory - two electric and two gas - may have exploded.

It was understood a group of about ten people were holding a meeting in one of the upper floors at the time of the explosion.

An RAF Sea King rescue helicopter from Leconfield, in East Yorkshire, ferried specialist dog teams and handlers to the site.