Some 135 people were killed in a crush at a soccer stadium in southeast Guinea on Sunday, a local group of human rights organisations said, sharing an estimated death toll more than twice as high as the official toll of 56.

A controversial refereeing decision sparked crowd violence and tear gas volleys from police during the match in the town of Nzerekore, leading to a deadly scrum as spectators tried to flee.

A collective of human rights groups in Nzerekore region said on Tuesday its higher estimate was based on information from the hospital, cemeteries, witnesses at the stadium, families of victims, mosques, churches, and the local press.

"We now estimate 135 people died at the stadium, mostly children under the age of 18," it said in a statement, adding that over 50 people were still missing.

The group blamed security forces for using excessive tear gas and prioritising the protection of officials over spectators.

It also said vehicles carrying officials and others escaping the stadium had struck spectators as they tried to flee what it described as an overcrowded venue whose gate was being obstructed by security forces.

It said it held the tournament organisers responsible as well as Guinea's ruling junta, as they provided technical and financial support for the event honouring military leader Mamady Doumbouya.

The government, which promised on Monday to launch an investigation, has not responded to the group's statement.