(CNN) Sometime Friday morning, Canadian officials will give the signal and a convoy of hundreds of vehicles will roll south, through the battered city of Fort McMurray, as evacuees try to get away from the flames of a massive wildfire.

Officials said the effort will involve 400 cars and a helicopter that will fly ahead to make sure the path is safe.

On Thursday it wasn't safe, and thousands of people who lived north of the city had to be flown over the fire that has torched 850 square kilometers (328 square miles).

The wildfire burns through northern Alberta in this image released by NASA on May 3.

The wildfire burns through northern Alberta in this image released by NASA on May 3.

The wildfire rages through Fort McMurray on Tuesday, May 3.

The wildfire rages through Fort McMurray on Tuesday, May 3.

A helicopter flies past the wildfire in Fort McMurray on May 4.

A helicopter flies past the wildfire in Fort McMurray on May 4.

Robert Parker, left, and Matt Jones siphon gas from two snowmobiles for their truck on May 4.

Robert Parker, left, and Matt Jones siphon gas from two snowmobiles for their truck on May 4.

Traffic is at a standstill on Highway 63 south as residents flee the wildfire on May 4.

Traffic is at a standstill on Highway 63 south as residents flee the wildfire on May 4.

Evacuees watch the wildfire near Fort McMurray on May 4.

Evacuees watch the wildfire near Fort McMurray on May 4.

People camp out at a beach south of Fort McMurray on May 4.

People camp out at a beach south of Fort McMurray on May 4.

The wildfire moves toward the town of Anzac on Wednesday, May 4.

The wildfire moves toward the town of Anzac on Wednesday, May 4.

A woman picks through donated clothing and goods at a makeshift evacuation center in Lac la Biche on May 5.

A woman picks through donated clothing and goods at a makeshift evacuation center in Lac la Biche on May 5.

Tyra Abo sits on a cot at a makeshift evacuation center in Lac la Biche, Alberta, on May 5.

Tyra Abo sits on a cot at a makeshift evacuation center in Lac la Biche, Alberta, on May 5.

A member of the Royal Canadian Mounted Police surveys wildfire damage in Fort McMurray. The RCMP tweeted the photo on May 5.

A member of the Royal Canadian Mounted Police surveys wildfire damage in Fort McMurray. The RCMP tweeted the photo on May 5.

Drivers wait for clearance to take firefighting supplies into town on Thursday, May 5, outside Fort McMurray.

Drivers wait for clearance to take firefighting supplies into town on Thursday, May 5, outside Fort McMurray.

A police helicopter lifts off through dust and smoke on May 6.

A police helicopter lifts off through dust and smoke on May 6.

The remains of a swing sits in a residential neighborhood destroyed by the fire on May 6 in Fort McMurray.

The remains of a swing sits in a residential neighborhood destroyed by the fire on May 6 in Fort McMurray.

A huge plume of smoke from the wildfires rises over Fort McMurray in this aerial photograph taken on May 6.

A huge plume of smoke from the wildfires rises over Fort McMurray in this aerial photograph taken on May 6.

Smoke and flames create a dramatic sunset near Fort McMurray on Friday, May 6.

Smoke and flames create a dramatic sunset near Fort McMurray on Friday, May 6.

Remains of a home in Fort McMurray are seen on May 7.

Remains of a home in Fort McMurray are seen on May 7.

A helicopter helping with the Fort McMurray wildfire takes off from a staging base near Conklin, Alberta, on May 7.

A helicopter helping with the Fort McMurray wildfire takes off from a staging base near Conklin, Alberta, on May 7.

Skeletons of patio furniture are seen on May 7.

Skeletons of patio furniture are seen on May 7.

Foundations of homes are all that remain in parts of a residential neighborhood in Fort McMurray on May 7.

Foundations of homes are all that remain in parts of a residential neighborhood in Fort McMurray on May 7.

A ball of flame rises behind abandoned vehicles on Highway 63 near Fort McMurray on Saturday, May 7.

A ball of flame rises behind abandoned vehicles on Highway 63 near Fort McMurray on Saturday, May 7.

Rodney Howse gets water at a donation center on May 8. The center was established to help evacuees who were forced from their homes by the wildfire.

Rodney Howse gets water at a donation center on May 8. The center was established to help evacuees who were forced from their homes by the wildfire.

Smoke fills the air as a police officer checks vehicles at a roadblock along Highway 63 leading into Fort McMurray on Sunday, May 8.

Smoke fills the air as a police officer checks vehicles at a roadblock along Highway 63 leading into Fort McMurray on Sunday, May 8.

Remains of a burned-out house sit near intact homes in Fort McMurray on May 9.

Remains of a burned-out house sit near intact homes in Fort McMurray on May 9.

Burned ground surrounds a sign welcoming visitors to Fort McMurray on May 9. The wildfire began Sunday, May 1, and had torched nearly 617,800 acres as of May 10, according to Alberta's Wildfire Management agency. The cause of the blaze was unclear.

Burned ground surrounds a sign welcoming visitors to Fort McMurray on May 9. The wildfire began Sunday, May 1, and had torched nearly 617,800 acres as of May 10, according to Alberta's Wildfire Management agency. The cause of the blaze was unclear.

A police officer looks over a destroyed building in the Abasands neighborhood of Fort McMurray on Monday, May 9.

A police officer looks over a destroyed building in the Abasands neighborhood of Fort McMurray on Monday, May 9.

Charred remains of homes are seen in Fort McMurray on May 13.

Charred remains of homes are seen in Fort McMurray on May 13.

Canadian Prime Minister Justin Trudeau, left, and Fort McMurray Fire Chief Darby Allen look over the devastation during a visit to Fort McMurray on May 13.

Canadian Prime Minister Justin Trudeau, left, and Fort McMurray Fire Chief Darby Allen look over the devastation during a visit to Fort McMurray on May 13.

Burned trees dot the landscape in Fort McMurray on May 13.

Burned trees dot the landscape in Fort McMurray on May 13.

Remains of a building stand in the neighborhood of Abasand in Fort McMurray on May 13.

Remains of a building stand in the neighborhood of Abasand in Fort McMurray on May 13.

Remains of burned homes are seen in a neighborhood in Fort McMurray, Alberta, on Friday, May 13. A massive wildfire has forced more than 88,000 people from their homes.

They, like many who fled by car, ended up hundreds of miles away in Calgary, Edmonton and other Alberta cities.

When they will be able to go home is much in doubt.

"It will not be a matter of days," Alberta Premier Rachel Notley said. "The damage is extensive."

Notley said she knows her constituents are scared and worried about what they will find when the fires are out and they can go back.

"Trust us that we have your back, that we will be there for you. And that we will support you along the way," she said at an evening news conference.

Some good news

While the cause of the fire remains unclear, a dangerous mix of extreme temperatures and bone-dry conditions had fueled the inferno.

Chad Morrison, a senior manager for wildfire prevention with Alberta Wildfire, said the fire didn't move as much Thursday as it did Wednesday.

Strong winds didn't help, but lower temperatures -- after two days of record heat -- and lower humidity did.

The forecast for Friday included no rain, but winds were not expected to be as strong.

"We still have a few warm, hot burning dry days in front of us for sure. Firefighters will continue to be challenged," he said. "So we're not out of the woods yet and we still have a long ways to go."

Quick escapes

Cameron Spring had 30 minutes to pack up a lifetime of memories from the house he grew up in.

The fire, which started Sunday, was racing toward his home, destroying everything in its path.

"We had next to no warning," the 27-year-old said. "I was able to grab some clothes, toiletries, a hard drive and laptop, passport and my Brazilian jiujitsu belt."

Spring escaped just in time. His neighborhood -- more than 100 homes -- burned to the ground.

"Absolutely everything was leveled," he said. The only things left standing: burnt trees, a light post and a few chimneys.

But Spring doesn't have time to think about losing his home. He's also the safety and operations director at Phoenix Heli-Flight, which was busy evacuating hospital patients and helping firefighters by dropping water from the sky.

"It's not difficult at all to keep working and not think of it," he said. "Just knowing that everything we lost is replaceable is comforting."

One of the people his outfit rescued was Peter Fortna, who with his cat, Sami, and his roommate, had fled about 11 kilometers (6.8 miles) down the road to a friend's house.

A Phoenix pilot thought the area was in danger, so he set his helicopter down in a field when he saw Fortna and others nearby.

The pilot told them it was time to move to safety again and offered to take them to the airport, which was about a minute away by air. There, Fortna rented a car and drove 435 kilometers (270 miles) to Edmonton.

"I never feared for my life, but it was close enough," Fortna said of his ordeal.

Shifting winds

Canada wildfire: By the numbers 1,600: Structures destroyed 88,000: People evacuated 850: Square kilometers burned 250: Firefighters 12: Firefighting helicopters 0: Reported fatalities

Not everyone left in a timely manner, Sgt. Jack Poitras, a spokesman for the Royal Canadian Mounted Police, told reporters Thursday.

"We still have some people who have been hanging around," he said. That included two whom police discovered in town Wednesday night.

Officers are going into accessible areas and looking for signs of people, he said.

Figuring out where the fire is headed is very difficult, he said, because the strong winds kept shifting.

"It's very dangerous because it keeps going back and forth," he said.

The flames also prevented people north of the city from being able to travel south.

"It's not safe to let them through," Poitras said.

1,600 structures destroyed

The mammoth inferno has torched at least 1,600 structures, Notley said earlier. She later noted that figures couldn't be updated Thursday night because fire fighters were too busy battling the fire.

CNN Map

Authorities ordered the evacuation of more than 88,000 people -- including everyone in Fort McMurray.

The northeastern Alberta city isn't the only area on fire. At least 49 wildfires are burning in Alberta , the provincial government said.

On the run again

Many who heeded the evacuation orders had to flee a second time as the unpredictable fire headed toward an emergency shelter in Anzac.

Donna Guillamot was one of tens of thousands evacuated from the Fort McMurray area to Anzac this week.

"I thought it was safe here, so I guess we'll go to Edmonton," Guillamot told CBC News. "Now you're sitting here and all you see is red flames. It's pretty scary."

Authorities are still trying to evacuate thousands of residents.

"Crews successfully evacuated 4,000 people from the camps north of Fort McMurray, and we are optimistic that this number will reach 7,000 by the end of day," Alberta Premier Rachel Notley said Thursday.

'Quite an amazing effort'

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Spring said he's amazed by the generosity of strangers from all over Alberta province.

The wildfire destroyed gas stations, leaving many drivers and evacuees stranded. So fellow Canadians drove up a clogged highway, giving away gas, food and water.

"That's the most emotional part of it -- everyone else coming to help you," he said. "It gives you hope ... not everything's going to be bad."

A punk band from Pittsburgh, Pennsylvania, that was supposed to play a show Thursday night in Fort McMurray will instead play a benefit show in Edmonton.

Anti Flag asked people to chip in at least $5 each for the Thursday all-ages show.