State-run oil company Pemex, initially reported that three workers were injured but later raised the number.
"We regret to inform that at the moment the current number of injured from the accident ... is 30," the company tweeted.
Pemex said the explosion took place at the Clorados 3 plant of Petroquimica Mexicana de Vinilo. It added that the plant is operated by another company, Mexichem, with which it has an association.