MEXICO CITY, July 5 (Xinhua) -- Back-to-back explosions at a small fireworks factory in central Mexico has killed at least 24 people, including one minor, and injured 49 on Thursday, local authorities said.

Four blasts ripped through the factory on the outskirts of Tultepec, a town north of Mexico City, 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.

Helicopters took the wounded to several hospitals and more than 300 police were sent to the scene.

The government of the Mexico State said that 17 people died at the scene and seven died later at the hospitals. At least two police officers and four firefighters were among the victims.

"We deeply regret the deaths, including those of fellow firefighters and police officers who saved many lives in exchange for their own," the state's Red Cross office tweeted.

Video images showed a massive plume of smoke rising after the explosion. Reporters arriving later found wrecked buildings and scorched ground in the town.

A fire triggered by the blasts was said to have been brought under control. The cause of the explosions are still under investigation.

Mexico's President Enrique Pena Nieto said via Twitter that he regretted "the loss of lives in the Tultepec explosion," and expressed his condolences to the families of the victims.

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 of people.

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.