Two siblings, ages 2 and 5, were carried away in the filthy, north-flowing river, which empties into the ocean just north of the U.S.-Mexico border, said San Diego Lifeguard Lt. Andy Lerum.

It is believed the children were with their parents in a Honda Civic that became trapped and carried away across the border and into the United States, The San Diego Union-Tribune reported. A third sibling, identified as 10- year-old Arami Muro Mendez, was found the same night in Tijuana, according to the newspaper.

On Sunday, the search for the two younger children was scaled back after authorities were unable to find a body reported by a migrant.

Sunday morning, Tijuana firefighters told San Diego lifeguards that an emergency call was received from someone who saw a body near Hollister Street and Monument Road, Lerum said.

Personnel and helicopters from several agencies searched the area for several hours and were unable to find any bodies, according to the lieutenant.

At 7 a.m. today, authorities planned to bring in a dog trained to find cadavers, the Union-Tribune reported.

"It's always tragic when you are searching for a person who has no chance of survival," San Diego lifeguard Lt. John Everhart told the newspaper.

"We're trying to bring closure to the family."