Brazilian authorities say a police gunbattle with inmates and their supporters trying to stage a mass escape from a prison in the country's north has left 20 people dead.

Public security officials in Para state have identified 19 of the dead as prisoners or their supporters at the Santa Izabel penitentiary in the metro area of the state capital of Belem. At least four people were injured.

The number of inmates who escaped Tuesday will only be published after a final tally is taken.

Police investigator Rodrigo Leao saytwo assault weapons, three pistols and two other guns were seized from a group who tried to break in to facilitate the prison break.

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This story has been corrected to show that the breakout attempt was Tuesday.