Authorities in Santiago have ordered a day of extraordinary anti-smog measures on 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.

It was adopted "due to poor wind conditions, with the objective of protecting the health of the population," the mayor's office said in a statement.

Last week the southern city of Temuco, another of the eight tournament host cities, declared an environmental emergency because of air pollution caused by wood-burning heaters.

The government has vowed not to let air pollution interfere with the continental football showcase, which runs through July 4 and is expected to draw some 750,000 fans.

Santiago, a city of seven million people, is one of the most polluted capitals in Latin America.

The last time authorities declared an environmental "pre-emergency" here was in July 2012.