He says it's not clear how many people were on the bus. "However, this does not match the number of people killed and injured", the ministry said. It was also not known if the driver was among them. In January, 52 people were killed in the country's worst road fatality in four decades.
With an unknown number of passengers on board, the police have been working closely with emergency services to search for survivors.
The accident took place before dawn Wednesday near a river in the coastal province of Camana. Three seriously injured passengers were to be transferred by helicopter to regional capital Arequipa, Civil Defence chief Jacqueline Choque said.
Local media reported that the coach was traveling from the town of Chala to the city of Arequipa when the vehicle fell from a height anywhere between 80 meters (260 feet) and 200 meters (650 feet).
Peru's President Pedro Pablo Kuczynski sent his condolences to the victims' families on Twitter.
Last month, a bus accident in the same highway left 51 people dead.
A bus is seen at the end of a ravine after veering off a mountain road and plunged into a ravine on the Panamerican road in southern Peru.
The toll from the Pasamayo crash matched that of an October 2013 accident in Cusco, southeast of Lima.