Beijing. The death toll climbed to 48 as search efforts continued in southern China on Thursday after a highway section collapsed in a mountainous area, sending more than 20 cars down a steep slope.

Officials in the city of Meizhou said three other people were unidentified, pending DNA testing. It wasn’t immediately clear if they had died, which would bring the death toll to 51.

The section collapsed after heavy rains and the Meizhou city government said that 23 vehicles have been found after a 17.9-meter (58.7-foot) long section of the highway gave way about 2 a.m. on Wednesday. Thirty other people had injuries, none of them life-threatening, a government statement said.

The search effort was complicated by steady rain, gravel and soil coming down at the site, posing some risk to the workers, a fire department official told Chinese media.

Rescue teams divided the area into 10 grids and searched with dogs and life-detecting devices, the report said. Excavators and cranes were also brought in to help.

The collapse left a barren scar down a steep slope in an otherwise verdant green forested area. Witnesses told local media they heard a loud noise and saw a wide hole open up behind them after driving past the section just before it collapsed.

Video and photos in local media showed smoke and fire at the scene, with a highway guardrail leaning down into the flames. A pile of blackened cars could be seen on the slope leading down from the highway.

A photo later showed a construction crane lowering a mangled car to the road surface, near three other similarly wrecked vehicles. All appeared to have been burned out.

Over 56 centimeters (22 inches) of rain has fallen in the past four weeks in the county where the roadway collapsed, more than four times as much as last year. Some villages in Meizhou flooded in early April, and the city had seen heavy rain in recent days.

Parts of Guangdong province have seen record rains and flooding in the past two weeks, as well as hail. A tornado killed five people in Guangzhou, the provincial capital, last weekend.

Heavy rain and flooding pose a special risk to mountain roadways and highway bridges because of erosion, debris flows and landslides. China has massively expanded its infrastructure in recent years, adding more than 1 million highway bridges, the world's largest network of high-speed trains and scores of new airports.

In the rush to build, flaws in design and construction methods have frequently come to light, while regular inspections and maintenance are sometimes given short shrift. Dozens have died in recent years in tunnel collapses and floods, including 14 who drowned in subway trains in the central city of Zhenzhou during massive flooding that killed around 300 people.

Subsequent reports said the system had not been prevented with adequate and other equipment and that officials failed to suspend service as they should have under government directives.

China's overseas projects such as roads and dams under the Belt and Road Initiative have also been criticized for design problems and poor quality, potentially posing a challenge to its efforts to build its influence in the developing world.