Rescuers were today continuing their painstaking search for survivors of the Glasgow plastics factory blast, which has so far claimed seven lives.

The police today named four of the victims as Ann Trench, 34, of Colston, Glasgow; Margaret Brownlie, 49, of Glassford Road, Strathaven; Tracey McErlane, 27, of Westercommon Drive, Possilpark; and Peter Ferguson, 52, of Kilbarchan.

Strathclyde Firemaster Brian Sweeney said that 80 to 100 firefighters were still searching the remains of the Stockline Plastics factory, which was destroyed yesterday by an explosion thought to have been caused by an industrial gas oven.

Chief Superintendent David Christie said that two people were believed to be still trapped beneath the rubble.

Around 40 people have been confirmed as injured, seven of whom were pulled from the building. Fifteen are seriously hurt. All of those killed or injured were working in the factory at the time. Most were attending a meeting on the top floor.

The last survivor rescued was a young woman who had been able to communicate with her rescuers through the rubble. She was brought out at around 9pm yesterday after an nine hour ordeal.

Mr Sweeney said she had been found in "distressing circumstances" but was expected to make a full recovery. Rescuers also removed a body bag from the rubble early today.

Mr Sweeney told reporters at the scene that knocking noises had been heard at around 5am and sniffer dogs had also given indications that there may still be people trapped inside.

One member of the International Rescue Corps, an organisation more used to dealing with earthquake scenes, said: "This gives us fresh hope". However, others cautioned that it may just have been background noise.

Mr Sweeney said today: "Yesterday evening we put out a call for help across the United Kingdom for dedicated urban search and rescue specialists to assist us because we believe that that operation, that rescue operation will continue for several days.

"During the evening, sadly, we have discovered more fatalities in terms of people who have lost their lives. I can confirm to you that the death toll now stands at seven."

Health and safety inspectors had visited the factory two months ago and found no problems, a company executive said.

Eric North, a manager with Dundee-based Graham Plastics, a sister company of Stockline, said that the Glasgow factory was "very safety conscious". He added: "I simply cannot understand how this happened. There was a very strong safety regime."

Mr North rejected suggestions from local politicians that employees at the Glasgow plant had claimed that they had no channels to raise safety concerns. "That is total nonsense," he said.

However, trade union and political sources insisted that there had been complaints from employees about a lack of consultation over safety.

The explosion, which was heard across the city, caused walls to collapse, floors to give way and the factory roof to cave in. Cars parked outside were showered with falling masonry and glass, neighbouring buildings and shops shook and the surrounding streets were filled with a choking dust cloud.

Survivors said they thought the blast may have occurred in one or more of the gas ovens in the coating department of the factory, which makes window frames, ceilings and water tanks.

Daniel Gilmore, his head heavily bandaged and his face marked with small cuts, said about ten people were in the meeting at the time of the blast. " All of a sudden I heard a huge bang and then the roof fell in on us and everything went black. I couldn't see a thing," he said.

Shoppers and workers from nearby premises ran to try to help the injured. Stephen Anthony, a worker at a neighbouring factory, said: "I tried to help some of the injured but when the fire brigade arrived I was advised to stand clear," he said. "I could hear people screaming underneath the rubble, it was a horrible experience."

A spokeswoman for Transco said mains gas had not been a factor in the explosion. Strathclyde police established an emergency helpline on 0870 0501999.