A 10-month-old was found dead and three other people are missing after a raft carrying nine people flipped on the Rio Grande, authorities said Thursday, a day after the White House asked Congress for billions more in funding to secure the border.

The missing were described as two boys, ages 6 and 7, and a man.

"What we're dealing with now is senseless tragedy," said Raul L. Ortiz, chief patrol agent of the Customs and Border Protection's Del Rio sector.

"The men and women of the U.S. Border Patrol have been doing everything in their power to prevent incidents like this," he said. "And yet, callous smugglers continue to imperil the lives of migrants for financial gain."

Migrants often try to cross the river, mostly in poorly constructed rafts with no safety gear, and the water can be deceptively high and fast.

CBP said agents detained a man for allegedly illegally entering the United States at about 9:45 p.m. Wednesday near Del Rio, Texas. He told them that the raft carrying nine people had overturned and that his baby son and nephew had been swept away, along with the other child and the man.

The agents heard the man's wife and an older son screaming in the darkness, and the two were pulled from the muddy water alive, CBP said.

Another man and his 13-year-old child were rescued nearby, the agency said. The children were taken to hospitals for observation.

Border agents later found the infant's body several miles downriver, CBP said.

A record number of Central American families are crossing the border, some on foot and some via the river. Last week, border agents rescued 10 people in a sinking raft in the same area, including a 3-year-old who had become separated from her mother on the Mexican side.

CBP has reported that during the last budget year, rescue teams responded to more than 4,300 emergencies, which involved 283 deaths, including those who drowned or died in the desert. The high was in 2005, when 492 people died.

Officials at the Department of Homeland Security say the system at the border is straining under the surge in families, who require different care and have different needs from those who used to cross — mostly single men from Mexico.

The White House on Wednesday asked Congress for an additional $4.5 billion in funding for the border. Acting Homeland Security Secretary Kevin McAleenan told a Senate subcommittee Thursday that the department needed the supplemental funding to help manage the crush of migrants and to provide proper care.

But Democrats are wary of giving the administration more money, especially after the longest government shutdown in history over President Donald Trump's demand for border wall funding. Trump eventually declared a national emergency to circumvent Congress to get the funding elsewhere.

The new emergency funding wouldn't be used to build any of the wall, officials said.