Two people are in a critical condition in hospital after a gas explosion destroyed three flats.
The pair, who sustained serious burns, escaped from the wreckage with two others after the blast in Wigan, Lancashire.
Emergency crews were called to Blake Close in Worsley Mesnes when firefighters began a three hour attempt to extinguish the flames.
A Greater Manchester Police spokesman said the "top two flats in a block of three had concertinaed into the ground floor property".
He added: "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.
"A full search of the block of flats, including the ground floor flat, will be carried out by specialist search teams in the next few hours. The cause of the explosion is currently under investigation."
The scene has been extensively cordoned off for investigators to establish the building's safety and source of the explosion.
A spokesman for Greater Manchester Fire Service said four crews attended the three-storey building including a specialist emergency rescue group.
He said: "At the height of the incident 70 firefighters were involved. Two search and rescue teams are now ready to go in."
