Mexico's state-owned petroleum company Pemex said that the explosion occurred 3:15 p.m. (20:15 UTC) Wednesday at the Clorados 3 plant of Petroquimica Mexicana de Vinilo (PMV). The plant is in the state of Veracruz about 600 kilometers (373 miles) southeast of Mexico City.

Luis Felipe Puente, head of federal emergency services, said three people had died in the blast.

The governor of Veracruz state, Javier Duarte, told local television that more than 60 people were believed to be injured and said via Twitter that by evening the fire was under control.

Duarte said some areas near the plant had been evacuated, and recommended people remain indoors to avoid exposure to toxic fumes. Schools were ordered to remain closed Thursday.

The state-owned energy company claimed the threat to nearby residents was diminishing.

"The cloud that emanated from the PMV plant in Coatzacoalcos is dissipating rapidly, which means it is losing its toxic effects," Pemex said via Twitter.

The PMV, a vinyl petrochemical plant, is a joint venture between Pemex's petrochemical unit and Mexican plastic pipe maker Mexichem.

jar/rc (AP, Reuters)