(CNN) A 10-month-old boy was found dead and three people remained missing after a raft overturned on the Rio Grande during an attempt by smugglers to get migrants from Mexico into the United States, according to officials.

Officials were first alerted to the incident in the US Border Patrol's Del Rio region late Wednesday night by a man who was apprehended for illegally crossing the border. He told Border Patrol agents that he was part of a group that attempted to cross the river in a rubber raft that "capsized, spilling all of its occupants into the cold and fast-flowing waters," according to Customs and Border Protection.

"Unfortunately" some of the people aboard were "swept away when the raft turned over," said a Department of Homeland Security official. Others struggled to stay afloat and keep their heads above water, the official said.

The wife and 6-year-old child of the man who made the report were later rescued, but the body of his 10-month-old son was found several miles downriver. The 6-year-old boy was treated by medical personnel on site and then rushed to the hospital, according to CBP.

Agents were able to jump into the river and rescue some of the people involved. Five people were rescued and four were initially reported missing, one of whom was the 10-month-old. The search for the remaining three was ongoing as of Thursday evening.

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