At least 51 people were killed in Guatemala City on Monday when a bus crashed through a guard rail and plunged into a ravine, rescuers said, one of the worst road accidents in Latin America in years.

The municipal fire department said the bodies of 51 people were retrieved from the wreckage of the bus, which was carrying more than 70 people when it crashed off a bridge into a river contaminated with effluent.

Victor Gomez, spokesperson for the Volunteer Firefighters group that was involved in the rescue effort, confirmed that there were “51 bodies in the provisional morgue.”

Rescuers had already managed to extricate 10 injured people from the wreckage.

Guatemalan President Bernardo Arevalo expressed sorrow over the tragedy and declared an unspecified period of national mourning.

“Today is a difficult day for the Guatemalan nation,” he said.

The fire department said the driver lost control of the bus and collided with several small vehicles before plunging over the precipice.

“The bus kept going, broke through a metal railing, and fell into a ravine about 20 metres (65 feet) deep until it reached the sewage-contaminated river,” the department’s Carlos Hernandez told reporters.

AFPTV images showed lines of firefighters passing bodies pulled from the murky waters, which were filled with trash, up the slope on stretchers.

According to local media, the bus was travelling to Guatemala City from the town of San Agustin Acasaguastlan in the El Progreso department, about 90 kilometres to the northeast.

Communications Minister Miguel Angel Diaz said an initial investigation showed that the bus was 30 years old but still had a license to operate.

He said that the cause of the early morning accident was still unknown and that investigators were looking into whether the bus was overloaded with passengers.

Road accidents leading to dozens of fatalities are common in Central and South America.

In January 2018, 52 people were killed in Peru when a bus fell off a cliff onto a beach north of the capital Lima.

In Brazil, 54 people were killed in March 2015 in a tourist bus crash in the southern state of Santa Catarina.