Mexico City authorities are banning more than 1 million cars from the roads and offering free subway and bus rides to coax people from their vehicles as the megalopolis' first air pollution alert in 11 years stretches into a third day.

Officials are advising residents to limit outdoor activity due to high ozone levels that are nearly double acceptable limits.

Environment Secretary Alejandro Pacchiano said Wednesday that if conditions don't improve, further measures may be considered, such as suspending industrial activity at some factories.

Mexico City Mayor Miguel Angel Mancera told Televisa news that about 1.1 million cars in the capital and surrounding valley have been ordered off the streets under the restrictions.