Metro Vancouver issued a statement saying high concentrations of ground-level ozone are expected to persist throughout the weekend.
Residents are asked to avoid strenuous outdoor activities during mid-afternoon, when ozone levels are highest.
Infants, the elderly and those who have underlying medical conditions including lung and heart disease and asthma are at additional risk from exposure.
People in Metro Vancouver and the Fraser Valley are asked to stay indoors or contact a doctor if they experience chest discomfort, shortness of breath, coughing or wheezing.
The advisory is expected to remain in place until there is a change in the hot and sunny weather.