A blast at a natural gas well in Canada's Alberta province has injured 11 people, officials have said.

The explosion at the Husky Energy well, near the town of Edson, occurred during drilling operations just before 1200 local time (1900 GMT), police said.

Two of the injured, one in critical condition and the other stable, were expected to be airlifted to hospital, police said. No deaths were reported.

A fire resulting from the blast has since been extinguished.

The energy company was drilling for "sweet" gas, which does not contain deadly levels of hydrogen sulphide, Husky Energy spokesman Graham White told Reuters news agency.

The workers injured in the flash fire, a type of fire that erupts suddenly and quickly subsides, were contractors, Mr White added.

He said the explosion had occurred during "fracking", a process in which natural gas trapped in shale rock deep beneath the surface is obtained by pumping a mixture of sand, water and chemicals into the ground with high pressure jets.