SALEM - Smoke from multiple brush fires burning in Massachusetts on Tuesday caused air quality concerns north of Boston and forced schools in Salem to dismiss students early or relocate them.

Salem High School students were sent home at 11:30 a.m. "due to elevated smoke levels around the campus," and Horace Mann Laboratory School children were being relocated to Witchcraft Heights Elementary School, the district said.

"There is no danger related to the fire itself, the impact is from the smoke," Salem Public Schools said in a statement.

In Reading, Tuesday afternoon's "Downtown Trick or Treat" event was canceled because of the smoky air.

Air quality map in Massachusetts

A fire and smoke map from the Environmental Protection Agency showed multiple cities and towns with "unhealthy" air quality on Tuesday morning.

The communities shown to have unhealthy air quality were Lynn, Salem, Swampscott, Saugus, Wakefield, Wilmington and North Reading. Click here to see the air quality for your zip code.

When the air quality is unhealthy, the EPA says sensitive groups like those with heart or lung disease should avoid long or intense outdoor activities and consider moving indoors.

Fires in Massachusetts today

Salem police said Tuesday morning they were responding to a new brush fire in the Salem Woods between First Street and the golf course that was sending smoke into the city.

"Avoid outdoor activity in that area and close windows to maintain indoor air quality," police said.

There was also fire activity south of Boston. The Canton Fire Department said late Monday night it was battling a 31-acre brush fire by the Reservoir Pond and said helicopters would be dropping water on the flames Tuesday.

And in Middleton, firefighters said it could take days to put out a fire by Middleton Pond that had spread to 225 acres.