Chilean football coach Javier Roca on Sunday said "fans died in the arms of players" and claimed tear gas-firing police fatally "over-stepped" the mark in the Indonesian football tragedy which claimed at least 125 lives.

The disaster happened when fans of Arema FC stormed the pitch at the Kanjuruhan stadium after their team lost 3-2 to bitter rivals, Persebaya Surabaya.

Police said 323 people were also injured in what is one of the world's deadliest sporting stadium disasters.

"The most terrible thing was when victims came to be treated by the team doctor. About 20 people arrived and four died. Fans died in the arms of players," Arema coach Roca told Spanish broadcaster Cadena Ser.

"I'm mentally shattered. I feel a heavy burden, even a heavy responsibility."

Police, who described the unrest as "riots", said they tried to force the thousands of fans to return to the stands from the pitch and fired tear gas after two officers were killed.

Many of the victims were trampled or choked to death, according to police.

The stadium holds 42,000 people and authorities said it was a sell-out. Police said 3,000 people stormed the pitch.

The 45-year-old Roca, who has spent a large part of his career in Indonesia, described how the full extent of the tragedy unfolded in the immediate aftermath of the game on Saturday night.

"After the match, I went to the dressing room, and some players stayed on the pitch. Returning from the press conference, I saw the tragedy," he added.

"The boys passed by with victims in their arms. Results dictate us and determine what happens in the end. If we were drawing, it wouldn't have happened."

Roca accused police of over-reacting and that the stadium was woefully under-prepared.

"It was proved that the stadium was not ready, they didn't expect such chaos. Nothing like this had ever happened at the stadium, and it fell apart because of the number of people who wanted to escape," added Roca.

"I think the police overstepped their mark, even though I wasn't out there and didn't experience the outcome.

"But looking at the images, they could have used other techniques. There is no result in a match, no matter how important, that is worth losing a life."