PHNOM PENH, Cambodia — Rescuers trawled a muddy river today for more bodies and Cambodia prepared for a day of mourning following a stampede by thousands of festival-goers that left at least 378 dead and hundreds injured.

A panic-stricken crowd — celebrating the end of the rainy season on an island in a river — tried to flee over a narrow bridge in the capital of Phnom Penh late Monday. Many people were crushed underfoot or fell over its sides into the water. Disoriented victims struggled to find an escape hatch through the human mass, pushing in every direction. After the stampede, bodies were stacked upon bodies on the bridge as rescuers swarmed the area.

The search for the dead in and along the river continued today as horrific footage of the night before aired on state television, showing twisted bodies — both alive and dead — piled on one another. Some writhed as they desperately reached out with their hands, the footage showed, screaming for help and grasping for rescuers who struggled to pull limp bodies from the pile as if they were trapped in sand or snow.

Paul Hurford, an Australian who runs a charity training firefighters in Cambodia, said he and several colleagues were called in not long after the stampede occurred. He said all they could do was quickly pick out the dead from the living and try to help the survivors.

“I’ve never come across something with such mass casualties ... in such a small area,” he said. “This was a devastating situation, no matter how you look at it.”

Cambodia’s prime minister called it the country’s biggest tragedy since the murderous 1970s reign of the Khmer Rouge.