MEXICO CITY, July 5 (Xinhua) -- The death toll from back-to-back explosions on Thursday at a small fireworks factory in central Mexico has climbed to 24, local authorities said.

The number of the injured also rose from an initially reported 40 to 49.

A total of 19 people, including police officers and firefighters, were killed by the blasts in Tultepec, a town just north of Mexico City, and five of the injured later died at hospital.

The government of Mexico State said several police officers and firefighters, who were at the scene when subsequent explosions occurred, were also among the fatal victims. One minor was also among the dead.

Four blasts ripped through a factory on the outskirts of Tultepec starting at around 9:40 a.m. local time (1440 GMT). Police, firefighters and rescue workers were at the site when three other explosions occurred some 20 minutes after the first.

The cause of the explosions are under investigation.

Tultepec produces some 25 tons of firecrackers and fireworks each year that are sold around the country, especially in the lead up to Independence Day celebrations in September.

In the past two years, explosions at licensed and makeshift factories, and the local fireworks market have killed scores.

Barely a month ago, on June 6, seven people were killed, eight injured and nearly 100 homes damaged after an illegal cache of gunpowder exploded.

The worst incident occurred in December 2016, when firecrackers and fireworks were unintentionally set off at one of the market stalls, sparking a chain reaction of explosions that killed 42 merchants and customers.