Eight people were in critical condition in hospitals while four were stable, Antique Governor Rhodora Cadiao told DZRH radio station.
The number of confirmed deaths was lower than the 28 reported earlier in local media.
The passenger bus from Iloilo province was on its way to the town of Culasi in Antique on Tuesday afternoon when its brakes malfunctioned on a winding road and it plunged down 30 m (98.5 feet) into a ravine, Cadiao said.
"We call that area the killer curve. It was already the second bus that fell off there," Cadiao added.
Retrieval operations have stopped after all visible bodies on site were already pulled up, the provincial government of Antique said on Facebook.
The total number of passengers, first estimated to be 53, was yet to be verified, it added.
The Philippines is notorious for its lax regulation on public transportation and poorly maintained roads.