The chaos unfolded as supporters pushed through one of the access gates at the Monumental venue in Cuscatlan, around 25 miles north east of the capital San Salvador.

The stadium was hosting a premier division quarter final match between clubs Alianza FC and Club Deportivo FAS when tragedy struck.

Footage showed dozens of fans charge on to the field in what one first aid volunteer described as an "avalanche". The game was subsequently suspended.

"It was an avalanche of fans who overran the gate," said the member of the Rescue Commandos group.

"Some were still under the metal in the tunnel.

"Others managed to make it to the stands and then to the field and were smothered."

Around 500 people had attended the event, and 100 people were taken to hospital, Luis Amaya, civil protection director said.

The Salvadoran Soccer Federation - the country's equivalent of the FA - "expressed solidarity" with those affected.

"The Salvadoran Football Federation deeply regrets the events that occurred at the Cuscatlan Stadium," the organisation wrote on Twitter.

"It also expresses solidarity with the relatives of those affected and deceased in this incident."

President of FIFA, Gianni Infantino, also paid his condolences to the people who lost their lives in what he called a "tragic incident".

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El Salvador President Nayib Bukele said the National Civil Police and the Attorney General's Office would conduct a "thorough investigation" into the events at the stadium.

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

Some of those hurt received medical treatment on the pitch, with the match suspended after just 16 minutes.

Police said a criminal investigation would take place in partnership with the attorney general's office.