Thirteen people are dead and another 18 are missing following the explosion at a petrochemical plant part-owned by Petroleos Mexicanos (Pemex) . The state-owned oil company, which said a fire led to the explosion on 20 April, confirmed that 136 people were also injured during the blast.

Pemex CEO Jose Antonio Gonzalez Anaya told Radio Formula that 24 people remain in hospital, including 13 in critical condition. Gonzalez Anaya flew to the site in Coatzacoalcos, Veracruz and said that rebuilding the plant may take a year, Bloomberg reported. The executive said it was unclear what caused the explosion.

"We know there was a leak, what we don't know is why, but everything points to an accident," Gonzalez Anaya said, according to Reuters.

Local and municipal police, along with marines, were charged with blocking the entrance to the plant, which was engulfed by the smell of ammonia in the air. According to Reuters, officials wore blue masks as family members crowded around and demanded information on missing relatives. Family members were notably not wearing anything to protect them from the fumes.

"We are desperate because no one is coming out to show their face," 49-year-old Ancelma Cordero said. Cordero's 21-year-old brother is one of the missing workers and has reportedly not answered his mobile phone. She noted that she had waited overnight for information and was beginning to get a headache from the fumes.

"They told us we were breathing toxins and we should leave," Cordero said of the authorities. "But...if we leave, they could make the bodies disappear."

According to Reuters, the explosion occurred at a vinyl petrochemical plant jointly controlled by Pemex's petrochemical unit and majority owner Mexican plastic pipe maker Mexichem. "This is neither the time for excuses nor finding those to blame," Juan Pablo de Valle, Mexichem's chairman, tweeted. "It is the time to tend to the injured, be accountable and support all those affected."

In a statement to the Mexican Stock Exchange (BMV), Mexichem said, "The emergency is being addressed and all emergency and evacuation protocols in coordination with Pemex, Civil Protection and with the support of the Emergency Response System CLAM supported by all companies in the region were activated."

State Governor Javier Duarte announced on 20 April that more than 2,000 people had been evacuated in the towns of Villa Allende, Nuevo Mundo and the surrounding suburbs, CNN Expansion reported.

The explosion is the latest incident in a series of mishaps for the company. A blaze killed a worker at the plant in February and a fire at a Gulf of Mexico platform led to seven deaths and $780m in losses.