Two people have been critically injured in an explosion which partially demolished a block of flats in Wigan.
Greater Manchester Police said the pair suffered serious burns when two flats collapsed in Blake Close, Worsley Mesnes, at about 2100 GMT on Saturday.
Two other people are suffering from the effects of inhaling smoke.
Police said specialist teams had searched the building and an investigation into the cause of the explosion had begun.
A police spokesman said the "top two flats in a block of three had concertinaed into the ground floor property".
He said: "Police officers helped evacuate residents from the neighbouring flats, which are all council-owned.
"At this stage, four people have been confirmed as being injured during the explosion.
"Two people suffered serious burns and are in a critical condition in hospital and another two are suffering from smoke inhalation."
Another four people were taken to Wigan Royal Infirmary suffering from asthma, angina and panic attacks.
Fire officials have said they were looking into the possibility there may have been a gas explosion.
Smoke inhalation
Police said they did not think anyone was still trapped at the scene but a full search of the site had yet to be carried out.
Some 70 fire fighters were there at the height of the incident, but by 0130 GMT the fire was said to be under control. Fifty fire fighters remained at the scene.
Three ambulances also attended, along with two paramedic fast response vehicles. People were treated at the scene for smoke inhalation and shock.
Meanwhile, an investigation is under way, with gas engineers and fire officers examining the damage.
Gas has been isolated for the building, and switched off, so that dogs and rescue teams can go into the building.
Dogs from the fire service's urban search and rescue team are being used to check if other casualties may still be trapped in the collapsed building.
John Aspinall, of Greater Manchester Fire and Rescue, said emergency officials were "questioning whether there has been some form of gas explosion".
'Painstakingly slow'
"There is no confirmation at present; however, there has been a large explosion which has demolished the second and first floor respectively of a block of flats on to the ground floor of the area," he said.
"Urban search and rescue teams are making an effective rescue into the scene... but it's painstakingly slow."
Paul Kudray, of the North West Ambulance Service, described the rescue effort.
He said: "You could imagine there was quite a scene of devastation which is quite difficult for both the casualties and obviously for the responders and rescuers."
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