Rescuers are continuing to search for two men in the rubble of the Stockline Plastics factory in Glasgow.
An aerial picture shows the extent of the devastation
Police and fire chiefs are optimistic that they will be found alive after the explosion which claimed seven lives.
Those who died have been named as: Ann Trench, 34; Margaret Brownlie, 49; Tracy McErlane, 27; Peter Ferguson, 52; Annette Doyle, 24; Thomas McAulay, 41; and company director Stewart McColl, 60.
Specialised heavy lifting gear has been brought in to stabilise the structure.
Prime Minister Tony Blair has expressed his sympathies for those affected by the blast and Scotland's First Minister Jack McConnell has visited the site.
Chief Superintendent David Christie said on Wednesday evening that 44 people had been injured.
Seven people have died and seven people have been rescued from the rubble during the operation.
"Further inquiries by the police indicate that we are looking for a further two people who we believe may still be within the incident site," he said.
"We must qualify that however by saying we still cannot account for anyone who was perhaps passing the premises at the time of the accident, or people who were perhaps in their cars outside the premises."
He stressed that it remained a rescue operation and voiced cautious optimism.
"Morale is high and we are very focussed and working flat out to try and work through the remaining debris to ascertain that there are only two people there.
"That is the focus and will remain the focus of this phase of the operation," he said.
It has been estimated that the rescue phase will continue until Saturday morning.
"Heavy lifting equipment has been brought in to stabilise the structure and remove part of the roof," added Chief Superintendent Christie.
Rescuers had hoped to reach more survivors after hearing knocking at 0500 BST.
Strathclyde's Firemaster Brian Sweeney said sniffer dogs had become "very excited" over several areas of the rubble.
Names of the dead
Police have released the names of the dead
(Pictured left) Tracey McErlane, 27, Westercommon Drive, Possilpark
(Centre) Margaret Brownlie, 49, Glassford Road, Strathaven
(Right) Peter Ferguson, 52, Kilbarchan
Ann Trench, 34, Colston, Glasgow
Annette Doyle, 24, Crowhill Street, Glasgow
Thomas McAulay, 41, Somerville
Drive, Mount Florida
Stewart McColl, 60, Halfway, West Kilbride
No more sounds have been heard, but he said the rescue effort would continue as long as they believed people were alive.
He later said he was "very optimistic" that the two missing men could be found alive.
Holes have been drilled in the masonry and microscopic cameras dropped down in the hope of spotting anyone still alive.
The companies in charge of the factory, ICL Plastics and Stockline Plastics, have released a statement expressing condolences to the families of the dead and injured staff.
"The cause of the apparent explosion and extensive damage to the buildings has not been confirmed," it went on.
They thanked emergency crews, hospitals and the local community for their help following the blast.
Barrie Brannan, Red Cross emergency response co-ordinator, said her teams were preparing to continue their operation throughout Wednesday night and into Thursday, if needed.
She added: "The teams are dealing with very high emotional states, providing emotional and practical support for the traumatised people at the centre. We have further volunteers on stand-by should they been needed over coming hours."
Stobhill Hospital - 13 discharged
Glasgow Royal Infirmary - three serious, five stable, one comfortable, two discharged
Western Infirmary - six serious, four discharged
Southern General - one serious, two comfortable, two discharged
Victoria Infirmary - one comfortable
Five pallets of bottled water, some 4,800 litres, were dropped off at the scene for rescue workers, many of whom have been suffering from heat exhaustion as they laboured with heavy equipment in warm temperatures.
The fire crews are being aided in their search by specialist dog teams from RAF Waddington near Lincoln and 11 members of the International Rescue Corps, based in Grangemouth.
Julie Ryan, of the International Rescue Corps, said the search for survivors was "very laborious".
"We are moving the debris bit by bit, shoring up parts of the building that may potentially collapse.
"The last thing we want to do is to injure or trap any of our rescue
Cause under investigation
Ms Ryan said that the organisation was using a Trapped Person Locator to
listen for signs of life, a carbon dioxide analysis which probes the rubble for
exhaled air from unconscious victims and a camera probe.
"We never give up hope. We always attempt to try and find people for as long as possible."
SEARCHING FOR SURVIVORS IN THE COLLAPSED FACTORY
1: Rescuers lower carbon dioxide monitors into cavities to check for breathing
2: Sensitive sound equipment detects vibrations which the human ear cannot pick up
3: People in collapsed buildings can survive for days in pockets formed by sturdy items such as drinks machines or filing cabinets
The explosion which destroyed the four-storey building in Grovepark Road, Maryhill, occurred shortly after 1200 BST on Tuesday.
The cause is under investigation, although eyewitnesses reported that an industrial gas oven had exploded.
Strathclyde Police confirmed that five people died at the scene and two died in
the Western Infirmary in Glasgow.