The Papua New Guinea government led by Peter O'Neill has occupied Prime Minister Sir Michael Somare's office, forcing him out of the building.
PNG has been in the grip of a political deadlock since Monday with both Mr O'Neill and Sir Michael claiming to be prime minister.
This was triggered by a Supreme Court decision to reinstate Sir Michael as the prime minister.
The unprecedented situation has prompted extra police to be flown into the capital Port Moresby to help ensure law and order.
Sir Michael has refused to step down and issued a statement, calling Mr O'Neill's actions illegal in a country which now has two rival prime ministers and two governor-generals.
Sir Michael has not been seen in public since Wednesday and his grip on power may be slipping, with his ejection from Morauta House and 20 heavily armed police loyal to his leadership deserting him on Friday.
The capital is reported to be quiet, with residents and businesses carrying on as normal.
Mr O'Neill says he is pleased to announce that the police have taken control of the situation in Port Moresby.
Mr O'Neill, backed by 75 MPs, told reporters outside Morauta House that by occupying the building he ended any uncertainty over who was in control.