Updated: 11.30
The warning came from officials who have been desperately organising evacuation convoys away from fire-ravaged Fort McMurray.
People are being rushed away from their destroyed and threatened homes, through scorched landscapes and down roads flanked by soaring flames.
Military and police are running the latest procession of hundreds of vehicles - and a mass airlift of evacuees is also resuming.
Yesterday, some 8,000 people were flown out and today authorities say another 9,500 are expected to be evacuated.
More than 80,000 people have already left Fort McMurray, which lies in the heart of Canada's oil sands.
The fire has destroyed 1,600 homes and other buildings and forced as much as a quarter of Canada's oil output offline, hitting worldwide oil prices. The region has the third-largest reserves of oil in the world behind Saudi Arabia and Venezuela.
Alberta's provincial government, which declared a state of emergency, said the size of the blaze had grown to 1,000 square kilometers (386 square miles). No deaths or injuries have been reported.
Chad Morrison, Alberta's manager of wildfire prevention, said there was a "high potential that the fire could double in size" by the end of Saturday.
But he expected the fire to expand into a more remote forested area northeast, and away from Fort McMurray.
Extremely dry conditions and a hot temperature of 27C are expected for the day, along with strong winds, he said.
Mr Morrison said no amount of resources would put this fire out, and what was needed was rain. "We have not seen rain in this area for the last two months of significance," Mr Morrison said. "This fire will continue to burn for a very long time until we see some significant rain."
Environment Canada forecast a 40% chance of showers in the area on Sunday. About 1,200 vehicles had passed through Fort McMurray by late Friday despite a one-hour interruption when they were stranded due to heavy smoke, authorities said.
Jim Dunstan was in the convoy with his wife, Tracy, and two young sons. "It was shocking to see the damaged cars all burned on the side of the road. It made you feel lucky to get out of there," he said.
In Edmonton, between 4,500 and 5,000 evacuees arrived at the airport on at least 45 flights on Friday, airport spokesman Chris Chodan said. In total, more than 300 flights have arrived with evacuees since Tuesday, he said.
Alberta's government has approved a payment of $1,250 Canadian dollars (€850) for every adult evacuated from Fort McMurray to help with their immediate needs, as well as $500 (€340) for every dependent.
Prime Minister Justin Trudeau told Canada's parliament: "Homes have been destroyed. Neighbourhoods have gone up in flames. The footage we've seen of cars racing down highways while fire races on all sides is nothing short of terrifying."
