WASHINGTON — A baby boy died after plunging into the fast-moving waters of the Rio Grande River as his family tried to cross into the United States on a rubber raft, authorities said on Thursday.

Three other people, two of them children, were missing after the raft capsized on the US-Mexico border, US Customs and Border Protection said in a statement.

The group of nine people aboard is part of a massive wave of migrants – most from violence-wracked Central American countries – trying to enter the United States.

US President Donald Trump, who has made his call for a border wall a central plank of his presidency, has declared the influx a national emergency.

His administration has taken steps to deter would-be asylum seekers, many of them family groups with children.

Trump's latest proposal calls for charging fees for asylum seekers, among other moves to make it harder for migrants to stay.

The accident on the Rio Grande took place on Wednesday night, CBP said, calling it a "senseless tragedy."

Agents came upon a man who told agents that all nine people on the raft fell into the Rio Grande when the vessel flipped over.

His 10-month-old son and seven-year-old nephew were among those swept away.

An adult man and a girl were also missing, and the search was continuing.

The wife and six-year-old son of the man who reported the accident were found a short time later, struggling in the water, and were rescued by authorities.

The body of the baby boy was found several miles downstream. — AFP