Baggage handlers who were unloading an Air Canada plane at Melbourne airport have had to call the Metropolitan Fire Brigade after finding a mysterious powder in the cargo hold.

The substance was found loose among the bags and promopted an emergency response.

Fireighters donned protective gear and spent several hours undertaking safety checks before it was deemed safe.

An Australian Federal Police spokesman said the substance was eventually found to be non-hazardous and airport operations had returned to normal.