Canadian firefighters battling an out of control wildfire near the oil city of Fort McMurray, Alberta were reinforced Thursday with the arrival of nearly 500 Americans and South Africans.

The fire has spread to more than 566,200 hectares (1.4 million acres), including 4,600 hectares in neighboring Saskatchewan province, although it has started to retreat from populated areas.

A total of 2,054 firefighters have been dispatched to the remote northern oil sands region -- an area that holds the world's third largest oil reserve -- to keep the flames at bay.

They include 200 American and 280 South African firefighters who went at Ottawa's request.

They have been assisted by 88 helicopters, 256 pieces of heavy equipment and 25 air tankers.

Some 100,000 residents of Fort McMurray and nearby towns and oil camps, are meanwhile planning their return home starting June 1, almost a month after being ordered to evacuate.

"You are returning to a community that was profoundly affected by a wildfire. Services that you are used to or rely on may be limited for some," authorities warned in a statement.

"If you're driving back, consider arriving with basic necessities to last for up to 14 days including food, drinking water and prescriptions."

Oil workers also are starting to return to facilities north of the city this week to restart oil production.

Officials also said the Fort McMurray airport has been scheduled to reopen for commercial flights on June 10.