"Today a historical maximum temperature record was established for Mexico City," director-general of the National Water Commission (Conagua) German Martinez Santoyo wrote on social media site X.

"The 33.9 degrees Celsius that had been reached on May 9, 1998 was surpassed by the 34.2 registered today at the Meteorological Observatory of Tacubaya," he added.

Mexico's capital and its metropolitan area together have more than 20 million inhabitants.

The mayor's office issued an alert over the high temperatures, which are expected to continue in the coming days. Authorities recommended the public stay hydrated, try to remain in the shade and use sunscreen.

Nearly all of Mexico has been hit by the heatwave, and in eight states with coastlines on the Pacific and the Gulf of Mexico, temperatures are forecast to exceed 45 degrees Celsius.