A stampede at a soccer stadium in El Salvador on Saturday left 12 people dead and hundreds of others injured, officials said.

The deadly crush happened as fans reportedly pushed through an access gate during a Salvadoran league quarterfinal match between clubs Alianza and FAS at Monumental stadium in Cuscatlan.

"El Salvador is in mourning," said a statement from the press office of Salvadoran President Nayib Bukele.

Carlos Fuentes, spokesman for the first aid group Rescue Commandos, said aid workers attended to more than 500 people and that more than 100 were taken to hospitals, some with serious injuries.

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fans in stadium after stampede

At least nine people were killed and dozens more injured when stampeding fans pushed through one of the access gates at a quarterfinal Salvadoran league soccer match between Alianza and FAS.  (AP Photo/Milton Flores)

The National Civil Police said that two of the injured were in critical condition.

Alianza fan José Ángel Penado told The Associated Press that the stadium closed its gate at 7 p.m., about 30 minutes ahead of kickoff, to fans who held tickets to the match.

"People got angry. We asked them to let us in, but no. So they knocked the gate down," Penado said.

A commotion in the stands began just 16 minutes into the match, with fans waving frantically as others carried the injured out of a tunnel and down to the pitch. The match was subsequently suspended.

aid workers carrying woman on stretcher

An injured fan in carried to the field of Cuscatlan stadium in San Salvador, El Salvador, on Saturday. Officials said more than 100 people were hospitalized. (AP Photo/Milton Flores)

A volunteer with a first aid group described the chaos to journalists as an "avalanche" of fans who apparently burst through a gate into the stadium.

The aftermath of the stampede was broadcast on live television. 

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Dozens of fans were seen receiving medical treatment on the field as the fans who escaped the crush stood on the pitch waving shirts over those apparently lying unconscious on the grass.

bodies covered with blankets at stadium

Bodies are covered with a blanket at the field of Cuscatlan stadium in San Salvador, El Salvador, on Saturday. Officials said the events of the disaster will be investigated and those responsible will be punished. (AP Photo/Milton Flores)

El Salvador President Nayib Bukele tweeted that there will be an "exhaustive investigation" of the disaster.

"Everyone will be investigated: teams, managers, stadium, ticket office, league, federation, etc," Bukele wrote. "Whoever the culprits are, they will not go unpunished."

The Salvadoran Soccer Federation said in a statement that it regretted what had happened and voiced support for the victims' families.

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Cuscatlan is about 25 miles (41 kilometers) northeast of San Salvador.

The Associated Press contributed to this report.