The search continues for four people missing after two boats crashed and sank on the Colorado River, ejecting more than a dozen people, authorities said.

A recreational boat carrying 10 people and another vessel with six people on board collided head-on Saturday night on a well-traveled stretch of the river that marks the border between California and Arizona, the Mohave County Sheriff’s Office said.

Both boats sank, and passing boaters pulled crash victims from the water. Ten people were injured, with one in critical condition, authorities said.

The crash occurred between two popular marinas and near Moabi Regional Park, a well-traveled recreation area crowded with people enjoying the Labor Day weekend.

Three women and one man remained missing on Sunday, Mohave County Sheriff Doug Schuster said.

Helicopters were deployed, and authorities scoured the shoreline to try to find them. Divers were sent into the river’s waters, which can range from shallow to 30 feet deep.

“These efforts will continue until all of those who are missing and unaccounted for have been located,” Schuster told reporters Sunday.

The cause of the crash is being investigated. None of the boaters were wearing life jackets, which aren’t required but are recommended by authorities, Shuster said.

On Saturday night, authorities had to temporarily halt the search because it was too dangerous to put divers into the dark waters. Efforts resumed after daybreak Sunday, and authorities closed off the stretch of the river where the search was taking place.

“We have four parties unaccounted for and presumed submerged,” said Eric Sherwin, spokesman for the San Bernardino County Fire District in California, which was assisting in the search.

Some of those on the boats apparently were thrown into the water by the force of the collision or jumped, and were swept down the river.

“We had victims of this collision that were located 3 to 5 miles downstream from the original point of impact,” Sherwin said.