Oil refineries and power stations pumping acid air pollutants along Mexico's Gulf coast threaten to erase carved stone murals at the pre-Aztec ruined city of El Tajin, a scientist said on Sunday.

Air pollution specialist Humberto Bravo said acid levels in the air around El Tajin, in oil producing Veracruz state, were among the highest in Mexico.

El Tajin's architecture is famous for intricate reliefs, many depicting an ancient Mesoamerican ball game sometimes compared to basketball.

"If nothing is done, within 10, 20 or 100 years, the hieroglyphics will disappear," said Bravo, from Mexico's UNAM university.