Two of Massachusetts’ largest cities are under an air quality warning Friday as smoke from Canadian wildfires continues to drift through the Bay State.

The warning, which includes the cities of Charlemont, Greenfield, Orange, Barre, Fitchburg, Chesterfield, Blandford, Amherst, Northampton, Springfield, Milford and Worcester, is in effect until midnight Friday, according to the National Weather Service.

An air quality warning “means that particulate matter concentrations in the region could reach or exceed levels that are harmful to the health of sensitive groups,” the weather service wrote.

• Read more: Why climate change and wildfires could lead to more air quality alerts in Massachusetts.

According to the weather service, the air is unhealthy for sensitive children and adults, including asthmatics, people with lung or heat diseases and the elderly. Sensitive children and adults should avoid spending long periods outdoors, warned the meteorologists.

In a post on X, meteorologists attributed the poor air quality in some areas to wildfire smoke coming from Canada.

A record number of wildfires in 2023 forced more than 235,000 people to evacuate across Canada and sent thick smoke to parts of the United States, causing hazy skies and health warnings in several U.S. cities.

This report uses material from the Associated Press.