A leaking gas well exploded in west Edmonton Monday night, causing a fire shortly after about 700 residents of the Enoch Cree Nation had returned home following an overnight evacuation.

Officials say the explosion, sparked accidentally by workers trying to stop the sour gas leak at the Acclaim Energy Trust well, led to a small fire at about 10 p.m. local time.

Two workers were slightly injured and were treated at the scene.

Flames shot 20 metres into the air, and the fire was still visible Tuesday morning.

"Obviously it was unexpected, but the one positive, if you will, is that the emissions of sour gas have now been incinerated," Acclaim spokesman Kerk Hilton said. "We're actively monitoring the site and would issue any further update if necessary, but we don't believe there's any imminent danger of public health."

Workers first noticed the underground leak at the well site at about 8:30 Sunday morning. The company believes the leak may have been caused by a ruptured casing.

A watery brew of gas, mud and other fluids bubbled to the surface Sunday afternoon.

In all, officials said the site was leaking about one million cubic feet of gas a day. That would be enough to power seven average Alberta houses for 12 months.

Officials decided to evacuate homes in the area because of concerns that people could breathe in a toxic combination of natural gas and hydrogen sulphide, which can make people dizzy and cause trouble breathing.

A nearby secondary highway was closed and everyone living within 1.5 kilometres of the well site was told to leave.

Most were put up in hotel rooms for the night, courtesy of Acclaim Energy.

Late Monday, about 700 people were allowed to return home, though the evacuation order still applied to about 20 families living nearest the well site.