A smog advisory remains in place Friday in Toronto and most of Ontario.

The advisory was issued Thursday afternoon by the Ministry of Environment, covering southern and eastern Ontario and some central regions.

Increasing cloudiness with scattered precipitation is expected over all regions on Friday.

Maximum temperatures are expected to remain in the high 20s to low 30s throughout most of the province.

The ministry says "Friday's air quality indices are forecast to be in the moderate to poor categories due to ozone and fine particles in the smog advisory regions." The situation is expected to improve on Saturday.

The ministry advises people to avoid strenuous exercise while smog conditions continue.

Smog is a hazy mix of pollutants made up of ground-level ozone, fine particulate matter and other pollutants. During the summer months, more than half of Ontario's smog-causing pollution originates in the United States.