The blast occurred around 3.30 p.m. on Wednesday at state oil company Pemex's Clorados 3 facility in the port of Coatzacoalcos, where authorities urged residents to remain indoors due to the presence of chemicals in the air that could cause skin burns, EFE news reported.
The explosion resulted in a cloud of gas and ash containing fibreglass and chloroethanol, the state government said.
Police shut down a stretch of the federal highway linking Veracruz with the neighbouring state of Tabasco.
The Clorados 3 plant suffered a serious explosion on March 11, 1991, killing four people and injuring over 300 people. (IANS)