Lima, March 31 (IANS/EFE): At least 16 people were killed and more than 20 injured when a bus plunged into a ravine in the Peruvian region of Ayacucho, officials said on Monday.

Thirteen people were pronounced dead at the accident scene and three others died while being treated at a hospital, Carlos Saravia, director of the health service in the city of Puquio, told Canal N television.

"The scene of the accident is a ravine and we can't get in there because it's about 500 metres and we don't have search and rescue gear," Saravia said.

There are "probably (more) people who need to be rescued" at the accident scene, but "their condition cannot be confirmed", the health official said.

"It's an area where these kinds of accidents always happen," Saravia said.

Rescue teams have been sent to the area, which was affected by torrential rains in recent days, highway patrol chief Orfiles Bravo told Latina television.

"Aiding the injured is difficult because of both the weather situation and the rough terrain," Bravo said.

Preliminary reports said the bus went off the highway at 5.30 a.m. on Monday. The cause of the accident has not been determined, officials said.

A crash involving three buses and a truck killed 37 people and injured 70 others last week on a highway about 270 kms north of Lima.

The accident rate in Peru's interior is extremely high due to the poor condition of roads, an obsolete bus fleet and drivers who obtain licenses on the "black market" by paying between $30 and $50, experts say.