An air quality alert because of smoke from wildfires in central Canada has been extended into Thursday morning for southern New Brunswick.
Until then, smoke from the plume may descend to the ground and reduce the air quality, the advisory from Environment Canada said.
According to the Air Quality Health Index, there is a "moderate risk" in smoke in the Fredericton, Moncton, Saint Andrews and Saint John regions.
There are hundreds of wildfires raging between northwestern Ontario and B.C.
The advisory was issued Tuesday morning as smoke was being carried over New Brunswick, and was expected to end "later Wednesday."
In an update issued around noon Wednesday, Environment Canada said the smoke plume had moved out of the northern areas but will persist over the southern part of the province into early Thursday morning, when the air quality forecast shows the risk returns to "low."
Wildfire smoke is a complex mixture of gases, particles, and water vapour that contains ozone, sulphur dioxide, nitrogen dioxide, carbon monoxide, volatile organic compounds and fine particulate matter, according to the federal government's air quality website.
"There is no evidence of a safe level of exposure for most of these pollutants," it says.
Some of the more serious symptoms of smoke exposure can include: dizziness, chest pains, severe cough, shortness of breath, wheezing (including asthma attacks), and heart palpitations (irregular heart beat).
Some of the people considered at higher risk of health problems when exposed to wildfire smoke include those with lung or heart conditions, seniors, infants and young children, pregnant women, people who work outdoors and people involved in strenuous outdoor exercise.