The death toll from a chain of explosions at a popular fireworks market on Mexico City's outskirts rose to at least 35 after two more people were added to the list, the local government said on Thursday.

The cause of the blast on Tuesday that struck the San Pablito open-air market in Tultepec, about 20 miles (30 km) north of Mexico City, several days before Christmas, remained unknown.

It was the third major explosion to devastate the market in just over a decade.

The number of people killed has increased to 35, the State of Mexico's government said in a statement. The latest confirmed victims were a woman and a girl, who both died in hospitals, the government said, noting that 26 people had died at the market, and another nine in hospitals. Dozens more were injured.

Witnesses described shocking scenes as they entered the blast zone to find burned bodies and dead children.

Video of the detonations showed a spectacular flurry of pyrotechnics exploding high into the sky, like rockets in a war zone, as a massive plume of charcoal-gray smoke billowed out.

The tragedy could weigh on the gubernatorial election in the State of Mexico next summer, where the ruling Institutional Revolutionary Party (PRI) aims to hold on to the populous region after a slump in President Enrique Pena Nieto's popularity.