Hazy smoke high above northern New England prompted health officials Monday to issue air quality warnings for most of the region.

The smoke came from dozens of forest fires in Quebec that sent a plume as far south as Washington, D.C., and led state officials in New York, New Jersey and Pennsylvania to issue health advisories.

The U.S. Environmental Protection Agency issued similar advisories Monday for northern New England, saying the haze carried particles that could cause problems for the elderly, children and people with respiratory or heart disease.

“Yesterday people were reporting that they’d actually seen ashes in the air,” said Steve Skinner, an airplane mechanic at the state airport in Berlin, Vt., on Monday.

The haze blanketed Vermont and New Hampshire over the weekend, keeping temperatures cooler than forecast, before drifting into Maine by Monday.

It covered the eastern two-thirds of Maine by Monday morning, according to meteorologist Mark Bloomer of the National Weather Service office in Caribou. In northern Aroostook County, visibility was limited to a mile, he said.

“It looks like downtown Manhattan in August,” he said.

The smoke was expected to move out of coastal Maine in the afternoon. But it could be back in Maine, New Hampshire and Vermont on Thursday and Friday, said Mark Breen, meteorologist at the Fairbanks Museum in St. Johnsbury, Vt.

“I’m kind of curious to see what will happen at the end of the week, when the winds turn to the north and northwest,” he said.

Maine’s Department of Environmental Protection advised the elderly, children and those with respiratory or heart disease to limit prolonged exertion.

“Certainly when you have a day like this, it makes sense for people who are vulnerable to be cautious about being outside,” said Dr. Lani Graham, acting director of the Maine Bureau of Health.

Neither the New Hampshire nor the Vermont health departments issued health advisories.

“It doesn’t mean we won’t say something if the smoke comes back,” said Linda Dorey, a spokeswoman for the Vermont department.

The EPA’s regional office in Boston warned that people in New England with a respiratory disease such as asthma should limit their outdoor exertion while the haze is present.

Many people who saw the haze thought it was simply fog. But Nick Santo, a flight instructor who owns North Ramp Aviation in South Burlington, Vt., said he could smell the smoke in the cockpit of the small single-engine planes he flew Monday.

“The smoke is just kind of smooth, pretty homogeneous, and in varying intensities,” he said.

At the Mount Washington Observatory in northern New Hampshire, staff saw and smelled the smoke beginning last Friday, said Katie Hess, a weather observer there.

“We definitely could see smoke not only here, but down in the valleys,” she said. “It kind of sits and hangs in the valleys.”

Visibility from the summit of the Northeast’s highest mountain was reduced to a half-mile at 2 a.m. Monday, she said. At its best, visibility was 35 miles over the weekend, when it normally would be 70 to 90 miles, she said.

By Monday, when the smoke had drifted into Maine, visibility had improved at Mount Washington.

“It’s still pretty hazy, although now it’s a mixture of smoke fires from Canada and haze from the cities to our south: Boston, New York, Hartford, everything,” Hess said.

The Quebec fires were set off July 2 by lightning and dry conditions in two separate regions southeast of James Bay between 200 miles and 400 miles north of the U.S. border. They have destroyed more than 250,000 acres of forest.