HALIFAX: Wildfires that have already forced thousands in Canada's Nova Scotia province to evacuate were threatening communities on the outskirts of Halifax on Wednesday and causing poor air quality hundreds of miles away as smoke drifted across the U.S. border.

Dozens of firefighters and several water bombers battled two out-of-control blazes - dubbed the Tantallon Fire and the Bedford Fire - northwest of downtown Halifax, the provincial capital. More than 18,000 people have fled their homes, most of them in the heavily forested fringes of the city, but there have been no reported fatalities.

Arid conditions and winds gusts of 25 kilometers an hour hampered firefighting efforts on Wednesday, making it "very dangerous for the folks in the field," David Steeves, an official with the Nova Scotia Department of Natural Resources, said at an afternoon news conference.

The two blazes were among the 14 wildfires burning in Nova Scotia, causing hazy skies and a general sense of anxiety across the Atlantic province, fire officials said.

"It's really been heartbreaking. There's definitely a lot of helplessness out there across the province right now," Premier Tim Houston said, urging residents to help others in need.

The wildfires were causing poor air quality hundreds of miles to the south in parts of the U.S. East Coast and Midwest as smoke drifts across the regions.

Air quality alerts were in effect for southern Michigan and Wisconsin, northern Ohio and parts of Pennsylvania, New Jersey and New York where a high concentration of pollutants were in the forecast, the National Weather Service (NWS) said.

"Sensitive groups should minimize strenuous outdoor activities," the NWS in Philadelphia said in a Facebook post along with a photograph of a hazy orange sun.

EVACUATIONS CAUSE GRIDLOCK

The 837-hectare Tantallon Fire, which is about 30 kilometres (19 miles) west of downtown Halifax, has damaged or destroyed about 200 homes and structures since it began on Sunday, officials said.

Closer to the city's center, in Bedford, families packed vehicles and raced out of the area, causing gridlock in normally quiet residential neighbourhoods after authorities issued a mandatory evacuation order due to the nearby fire and a potential ammonia leak.

"We know people are extremely, extremely distressed by what's going on. As a federal government we are there, we will be there to support," Prime Minister Justin Trudeau said in Ottawa. He pledged federal support for the Atlantic provinces, including Nova Scotia.

Forest fires also led to evacuations of about 400 homes in the neighboring province of New Brunswick over the weekend, officials said.

To the southwest of Halifax in Barrington Lake, another fire roared out of control on Wednesday. The fire covering more than 17,000 hectares has destroyed about 50 houses, fire officials said. The smaller Pubnico fire was ablaze about 30 km to the north of Barrington Lake.

Earlier this month, the western province of Alberta declared a state of emergency after tens of thousands of people were forced from their homes as unprecedented wildfires raged.