The official death toll from a stampede at a New Year's Eve evangelical vigil in Angola rose to 16 Wednesday, as witnesses said the tragedy was caused by a scramble for sachets of holy water.

"We confirm the death of 16 people, including four children, due to asphyxia, shoving and trampling of faithful at the entrance of Cidadela Stadium," Paulo Gaspar de Almeida, deputy commander-general of the Angolan police, told AFP.

Authorities probing how the disaster happened have discovered that the 80,000-seater stadium in the capital Luanda was packed to nearly double its capacity as turnout far exceeded expectations.

"The police, fire-fighters and health services and church leaders, all of us, were overwhelmed by the numbers of people who descended on Cidadela Stadium," said Gaspar de Almeida.

The initial death toll had stood at 10. Police did not give further details on the six latest deaths.

Worshipper Marcelina Baptista said people were crushed when they tried to grab sachets of water believed to have supernatural powers.

"The chaos began with the arrival of the last batch of people from Luanda's outlying neighbourhoods, through the entrance... where sachets of blessed water were placed. Everyone wanted to reach for one. That is what caused the stampede," she said.

The vigil was organised by the Universal Church of the Kingdom of God, which was founded in Brazil in 1977 and boasts of more than a million followers in Angola, according to the culture ministry.

Its overnight New Year's Eve prayer vigil in Luanda is an annual event.

The church has denied responsibility for the tragedy.

"We sought clearance to hold the service 20 days ago, and we were granted permission," Ferner Batalha, a bishop, told AFP.

Of the over 100 wounded during the crush, 25 sustained serious injuries, he said.