A 26-year-old man is in a critical condition following the blast just after 7am on Friday, while a 30-year-old woman also needed hospital treatment.
Police said the explosion was a result of “a deliberate act within the flat” in Kennedar Drive, Glasgow, which has been significantly damaged.
Twenty-three people in the block of flats were evacuated as a precaution while emergency services dealt with the incident but have since been allowed to return to their homes.
Police and other emergency services were called to the scene in the Govan area at around 7.05am on Friday.
The occupants of the flat were both injured in the blast.
The man was taken by ambulance to the Glasgow Royal Infirmary after sustaining burns while the woman was taken by ambulance to the city’s Queen Elizabeth University Hospital for treatment to minor injuries and has since been discharged.
Superintendent Craig Smith, of Greater Glasgow Police Division, said: “Enquiries carried out so far have revealed that the explosion was as a result of a deliberate act within the flat.
“The flat has been significantly damaged, however, the impact of the blast did not affect other properties in the block and the 23 people who had been evacuated have been allowed back into their homes.
“Kennedar Drive remains closed to vehicular traffic until further notice.”
Gas engineers went to the scene following the incident.
Bradley Barlow, spokesman for gas distribution company SGN, said: “Following reports of an explosion in Kennedar Drive in Glasgow, our engineers joined the emergency services on site earlier this morning.
“While it is too early to speculate as to what has happened, we have made the situation safe and we’ll work closely with the emergency services to help identify the cause.”
The fire service was also involved in dealing with the incident.
A Scottish Fire and Rescue Service (SFRS) spokesman said: “Operations Control mobilised three fire engines and an aerial appliance to the scene, where two casualties were assisted to safety and passed into the care of the Scottish Ambulance Service.
“A male casualty was transported by ambulance to Glasgow Royal Infirmary, and the female casualty was transported by ambulance to the Queen Elizabeth University Hospital.
“Residents were also evacuated from nearby properties as a precaution.
“SFRS crews have now left the scene after ensuring the area was made safe, and an investigation into the cause of the explosion is underway.”