India, July 16 -- Canadian wildfire smoke continued to block out the sun and turn skies yellow over states across the Northeast on Wednesday and pushing Massachusetts to issue an air quality alert warning sensitive residents to be careful.

As per the Massachusetts Department of Environmental Protection (MassDEP), air quality statewide is expected to be unhealthy for sensitive groups because of high levels of fine particles (PM2.5). MassDEP said, "Sensitive groups include people with heart or lung disease, such as asthma, older adults, children, teenagers, and people who are active outdoors."

The alert will stay in effect until midnight Thursday, according to MassDEP.

Smoke from a cluster of wildfires around western Ontario started cove...