Mexico City: A massive explosion at an oil facility in southeastern Mexico killed at least three workers, injured 30 more and triggered evacuations Wednesday, officials and state-run energy giant Pemex said.

A huge plume of toxic gray smoke could be seen spewing from the plant known as Pajaritos, in the city of Coatzacoalcos. The blast, which was felt from as far as 10 kilometers (six miles) away, forced the evacuation of nearby schools and businesses.

The cause of the explosion at the Petroquimica Mexicana de Vinilo (PMV) plant was not immediately known. The facility is jointly owned by Pemex.

Veracruz state governor Javier Duarte told Milenio Television that the blast killed three people at the plant. That was in addition to the 30 hurt, according to Pemex.

Duarte rushed to the scene of what he said was ‘a very strong explosion’ and fire crews were battling to bring the fierce blaze under control.

People living in the vicinity were ordered to remain indoors.

President Enrique Pena Nieto said on Twitter that the government would help the ‘affected workers and neighbours of the area.’

Fires at oil facilities in Mexico are fairly regular occurrences.

In February, two people were killed and at least seven injured in a blaze at a Pemex oil platform off the coast of Campeche, also in the southeast.