At least nine people were killed and four left missing when a bus and two other vehicles plunged into a ravine in a mountainous part of Costa Rica, the Red Cross reported Sunday.

The bus, car, and motorcycle slid into the 75-meter-deep (245-foot) ravine on Saturday when heavy rain caused a landslide at the El Hundimiento mountain pass, around 80 kilometers (50 miles) west of the capital San Jose.

Rescue services have pulled around 50 survivors, including the bus driver, from the gorge, according to the Costa Rican Social Security in charge of the country's public health services.

"As of now, we know of nine people who did not have vital signs," the Red Cross tweeted after the accident, adding that four people remain missing.

The bus was traveling between San José and Guanacaste Province with 47 people on board, the owner of the transport company, German Alfaro, told Costa Rican daily La Nacion.

The Red Cross had previously estimated the number of passengers at around 60.

Images shared by the rescue services showed the wreckage of the bus at the bottom of the ravine in a mountainous region where recovery efforts were particularly challenging.

Locals in the area said the accident was caused by a lack of protective barriers or signage along the road.

"We have been abandoned for years," Gilber Martinez told television station Canal 7.

But the government termed the incident "unpredictable".

"It is not the fault of the government or the bus company. It is something we cannot predict," Minister of Public Works and Transportation Luis Amador said.

Specialists from the University of Costa Rica released a report in March warning of the risk of road collapse in the area.

Costa Rican President Rodrigo Chaves declared three days of national mourning and said he will not attend the United Nations General Assembly in New York because of the emergency in his country caused by heavy rains.