El Salvador soccer fans were mourning Sunday after 12 people died and hundreds were injured in a stampede at a stadium, with the country's president vowing an investigation.

Authorities said initial reports pointed to a crush of fans who tried to enter the 35,000-seat Cuscatlan Stadium in the Central American country's capital San Salvador to watch a game between two local teams, Alianza and FAS.

The match was suspended as emergency personnel evacuated people from the stadium, where hundreds of police officers and soldiers gathered as ambulance sirens wailed.

Carlos Fuentes, spokesman for the emergency services group Comandos de Salvamento, said they were treating more than 500 people for various injuries, while civil protection authorities said 88 people in total were hospitalized.

The stampede started after a stadium gate fell, causing people to crowd together, Fuentes said.

Fredy Alexander Ruiz, a 28-year-old survivor, said he was "traumatized from seeing people thrown on the ground, dead, bruised, with their faces stepped on."

The stampede started 10 minutes into the game and after it was suspended even the players joined in the frantic rescue efforts.

"I had five people on top of me that were suffocating me," said Ruiz. "Thank God, I was able to grab the foot of a policeman, and he and a friend of mine pulled me out."

On Sunday night, dozens of Alianza fans set up a memorial to victims, placing a "Rest in peace" banner on the stadium wall, where they also left flowers and 12 candles to represent the dead.

After saying a prayer, the fans left, some of them in tears.

El Salvador's President Nayib Bukele said Saturday that authorities would investigate the incident and those responsible would be punished.

"Everyone will be investigated: teams, managers, stadium, box office, league, federation," Bukele said on Twitter.

He warned that "whoever the culprits are, they will not go unpunished."

- 'I couldn't even breathe' -

Survivor Sandra Guzman described chaos at the stadium in the moments the stampede began.

"A huge crowd of people fell on me. I couldn't even breathe, they were choking me," Guzman, 40, told AFP early Sunday as she was leaving the Rosales National Hospital.

When she was in front of the stadium gate that collapsed, she said, "people were pushing me to get in. They did not give me a chance to go back."

She panicked when people toppled onto her, Guzman said. "I fainted, and when I woke up I was in the hospital."

The Salvadoran Football Federation (Fesfut) said in a statement it "deeply regrets" the events that occurred at the stadium and "expresses its solidarity" with the families of those "affected and killed."

"Fesfut will immediately request a report of what happened and will communicate the relevant information as soon as possible," it said.

Due to the incident, the federation said "all soccer is suspended at the national level" on Sunday.

The chief of world soccer body FIFA offered his condolences after the "tragic" stampede.

The tragedy comes seven months after 135 people, including more than 40 children, were killed in a stampede following a football match in Malang, Indonesia.