Mexican environmental authorities said Friday that the pollution alert issued earlier this week for the capital region due to high concentrations of ozone in the atmosphere will continue for at least one more day.
The conditions prompting the Phase I alert are set to persist on Saturday, the Megalopolis Environmental Commission said in a statement.
While the megalopolis comprises Mexico City and 224 municipalities in the central states of Mexico, Hidalgo, Morelos, Puebla and Tlaxcala, the current alert applies to the sub-region of the Valley of Mexico Metropolitan Area.
The decision to extend the alert to a fifth day makes this the area's longest air pollution emergency since the period May 26-31, 1998.
The Phase I alert entails restrictions on vehicle use and a requirement that factories reduce emissions of ozone precursors by up to 40 percent.
Children, the elderly, pregnant women, and people with respiratory and cardiovascular problems are urged to remain indoors between 1 pm and 7 pm.
Authorities ordered 10 environmental alerts in 2016, two of which lasted for three consecutive days.