Border agents are searching for three children and an adult after their raft flipped on the Rio Grande as they tried to cross the U.S.-Mexico border, a law enforcement official says.

The missing included a 10-month-old baby, a 7-year-old boy and another child and a man. The number of migrant families crossing the U.S.-Mexico border has skyrocketed, and they sometimes try to traverse the river. The group made the attempt Wednesday evening near Del Rio, Texas when the raft overturned.

The official had direct knowledge of the incident but was not authorized to speak publicly and spoke to The Associated Press on condition of anonymity.

Border agents encountered the father, and rescued his wife and 6-year-old son. A second man and his 13-year-old son were rescued nearby.

Migrants often drown or need rescuing as they try to cross the river, which marks the international border between the United States and Mexico.

April and May are some of the most dangerous months to attempt to cross the river as its flow increases from spring run-off in the mountains of southern Colorado and northern New Mexico.

Record numbers of migrant families, mainly from Central America, are attempting to cross the Rio Grande, according to U.S. Customs and Border Protection data.