May 14 (Reuters) - A large wildfire is slowly

approaching the major Canadian oil sands city of Fort McMurray

and around 6,000 people in four suburbs have been told to

evacuate, local officials said on Tuesday.

The fire, fueled by tinder-dry conditions and high winds,

has been threatening the city in the western province of Alberta

since last week. It is now about 7.5 km (4.7 miles) away from

the Fort McMurray landfill, authorities said in an update.

They also expressed hope that a favorable wind shift was

expected Tuesday night, which could lead to winds from the

west-northwest pushing the fire away from Fort McMurray.

In addition to the harm that may befall people and

property, the fire puts a large portion of Canada's oil

production at risk. Fort McMurray is the hub for the country's

oil-sands output and a huge wildfire in 2016 forced the

evacuation of 90,000 residents and shut in more than 1 million

barrels per day (bpd) of output.

Alberta Wildfire Information Officer Josee St-Onge

earlier said the blaze grew significantly on Tuesday and noted

winds from the southwest were gusting as high as 40 km per hour

(24.8 mph).

"We're seeing extreme fire behavior. Smoke columns are

developing and the skies are covered in smoke ... firefighters

have been pulled from the fire line for safety reasons," she

told a media briefing.

The fire has grown in size and is now more than 20,940

hectares (51,740 acres), Alberta authorities said.

In a statement, the local authority said residents in the

suburbs of Abasand, Beacon Hill, Prairie Creek and Grayling had

to leave by 4 p.m. Mountain Time (2200 GMT).

People in other parts of Fort McMurray not under evacuation

order are also starting to leave, said resident Elsie Knister,

as she prepared to depart her downtown neighborhood on Tuesday

afternoon.

"People aren't waiting for an order, they're just going

already," Knister, who also evacuated in 2016, said in a phone

interview. "I feel sunk. I'm 71 and I don't want to go through

this again, it's horrible."

Officials said Fort McMurray is better prepared to fight the

fire than it was in 2016. Much of the boreal forest surrounding

the city burned in the 2016 fire, meaning there is less fuel

available to the blaze now.

"This fire activity is very different than (in) 2016 ... We

have an abundance of resources and we are well positioned to

respond to this situation," said regional fire chief Jody Butz.

He said evacuees were encouraged to leave Fort McMurray but

could remain in other neighborhoods in the city if they wished.

The city has 250 to 300 firefighters available to help protect

structures, Butz added.

OIL SANDS

Canada's oil sands industry produces roughly 3.3 million

barrels per day of crude, two thirds of Canada's total output.

Companies including Suncor Energy ( SU ), Canadian Natural

Resources Ltd ( CNQ ) and Imperial Oil ( IMO ) have oil sands

projects within 150 km of the city and many workers live in Fort

McMurray.

"This will put more people on edge, we'll have to see if the

actual production sites themselves come under threat," said

Martin King, an analyst at RBN Energy.

"Back in 2016 the fires themselves were getting close so the

companies evacuated people for safety, and of course the people

that worked in these sites were evacuated and had nowhere to go

so they ended up shutting down production."

In neighboring British Columbia, a wildfire burning near

Fort Nelson in the province's northeast grew in size but is

moving away from the town, offering some relief to around 3,000

residents who were forced to evacuate, the provincial wildfire

service said on Tuesday.