More cars were ordered off Mexico City's streets on Wednesday after a surge in pollution prompted authorities to issue the first air quality alert in 14 years.

President Enrique Pena Nieto convened a meeting of an anti-pollution commission after the city's government declared an "environmental contingency" on Monday due to high levels of ozone.

"The goal (of the meeting) is for them to find stricter measures to improve air quality and protect the health of more than 20 million Mexicans," Pena Nieto wrote on Twitter.

After older vehicles were kept off the streets on Monday and Tuesday, the Environmental Commission of the megalopolis decided to expand the ban on Wednesday to include all cars with license plates that have red stickers and end in the numbers three and four.

The commission, which was formed in 2013 to coordinate anti-pollution policies between the federal government, the capital and several surrounding states, said the ban was needed because vehicles produce 87 percent of nitrogen oxide and 32 percent of volatile organic compounds, both of which are ozone precursors.

The panel also agreed on a plan to improve the verification of vehicle emissions.

The extraordinary measures were imposed following an increase in ozone concentration, which can cause respiratory and heart ailments.

Officials urged people in the metropolitan area of 21 million people to avoid outdoor sports while kids and seniors were advised to stay indoors, in a city where a honking mess of more than 5.5 million vehicles chug along every day.

Federal authorities ordered factories in the greater Mexico City area to slash their emissions by 40 percent.

- Too many cars -

The last time the air quality emergency was issued was in September 2002.

The latest alert took residents by surprise as thick smog descended on the city just two days after the skies were unusually clear thanks to high winds that blew away hundreds of trees.

The alarm rang after ozone concentration surpassed the 190-point limit, surging to 194.

"There's no wind and this situation has not allowed the dispersion of pollutants," Tanya Muller, the city's environment secretary, told Radio Formula.

Muller lamented a Supreme Court decision that imposed changes last year to the city's "No Driving Today" program, which limits the number of days that older cars can be on the street.

The city must now take into account the levels of pollutants to impose restrictions on cars older than 2007.

The change, Muller said, has added 1.2 million more cars to the streets.

"We need to restrict vehicular traffic," Muller said.

- Former world pollution champion -

The pollution alert marks a reversal of years of progress made by the city to improve air quality after the United Nations declared the Mexican capital the world's most polluted city in the 1990s.

During that decade, ozone levels reached 398 points. The environmental contingency was declared 12 times in 1993 alone, according to the environmental commission.

Headed by left-wing mayors since 1997, the capital has launched various programs to reduce harmful emissions by modernizing the public transport system and encouraging the use of bicycles.

But Hector Riveros, a physics expert at the National Autonomous University of Mexico, said there are still hundreds of small buses known as "microbuses" and taxis that have pollution levels that are four to five times worse than cars.

The solution, he said, is to eliminate sulfur from gasoline, provide cleaner taxis and microbuses, and make speed rules more flexible so that "engines work more with maximum efficiency."