Authorities in Santiago have ordered a day of extraordinary anti-smog measures Friday, with a week to go before the Chilean capital hosts the opening match of the South American football championships.

Under the so-called "pre-emergency" declared by the Santiago mayor's office, more than 300,000 vehicles must stay off the roads and nearly 800 factories must remain closed.

The measures aim to combat the air pollution blanketing the capital and prevent it from clouding the Copa America, which kicks off next Thursday at Santiago's National Stadium with a match between the hosts and Ecuador.

The measure also bans burning wood or biomass fuels, suspends physical education classes at schools and recommends citizens forego outdoors athletic activities for a day.