Content warning: The following article contains details of a tragic bus accident in Guatemala, including fatalities and rescue efforts. Some descriptions may be distressing to readers. Discretion is advised.

At least 55 people were killed in Guatemala on Monday when a bus crashed through a guard rail and plunged into a ravine, authorities said, one of the worst road accidents in Latin America in years.

The bus was carrying around 70 people when it fell into a river contaminated with sewage in Guatemala City, creating difficult conditions for rescuers trying to retrieve bodies. 

"So far, 53 people have died at the scene," a spokesman for the public prosecutor's office, Moises Ortiz, told reporters.

Two others died after they were admitted, along with several other people, to the San Juan de Dios Hospital, spokeswoman Marlyn Perez said.

The bodies recovered at the site were taken to an improvised morgue in a nearby community hall where several distressed relatives went, fearing the worst.

Rosa Lopez told reporters that four of her nieces and nephews were thought to have been on the bus.

"When we heard about the accident on the news, we headed straight here," the 48-year-old said.

Injured passengers were taken to hospitals, many of them in serious condition.

Guatemalan President Bernardo Arevalo expressed sorrow over the tragedy and declared a three-day period of national mourning. 

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

Murky waters

The fire department said the driver apparently 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 meters (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.

"We're having a hard time with the rescue work," said firefighter Luis Quintanilla.

"We've been underwater for more than three hours trying to rescue the body of an apparently male person who is trapped between the twisted metal of the bus," he said.

The bus was traveling to Guatemala City from the town of San Agustin Acasaguastlan in El Progreso department, about 90 kilometers (56 miles) to the northeast, authorities said. 

"It's a huge tragedy, very painful," 40-year-old Marbelin Ortiz, a resident of the area near the accident site, told reporters.

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.

The public prosecutor's office said it had opened an investigation into the crash.

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.