Some non-certified indoor extension cords that were sold at discount stores in Ontario may cause fires or give people a shock, according to the province's electrical safety watchdog.

The Electrical Safety Authority said the cords were packaged in lengths of six, nine and 12 feet (1.8, 2.7 and 3.7 metres) and marked with the rating 10A-125V-1625W 16/2 SPT-2.

The ESA warns that the wire in the cords is undersized and may overheat, posing a fire hazard.

The cords are also improperly wired with reverse polarity, putting the user in danger of a shock hazard. The products have not been tested by a recognized certification agency.

The ESA says people should stop using the cords immediately.