Trump declared a national emergency at the US-Mexico border in February. (Representational)

A woman and her three children were found dead in a wildlife management area often used for illegal crossing into the United States from the border with Mexico in southern Texas, Hidalgo County sheriff said on Monday.

Sheriff Eddie Guerra wrote on Twitter, "Deputies are on scene by the river SE of the Anzalduas Park in Las Paloma Wildlife Management Area where Border Patrol agents located 4 deceased bodies. Bodies appear to be 2 infants, a toddler and 20yo female."

"Deputies are awaiting FBI agents who will be leading," he added.

Quoting the sheriff, Al Jazeera reported that the four may have been dead for a few days by the time they were discovered on Sunday in Las Palomas Wildlife Management area near the Rio Grande River.

However, their names have not been released so far and authorities are working to determine their country of origin.

Over a seven-month period ending in April, the US Border Patrol agents have caught more than 164,000 people along the border, surpassing the total apprehensions in 2018.

Raices, the largest immigration legal services non-profit organisation in Texas, has blamed the anti-migrant policies of President Donald Trump for the recent deaths along the border.

"Trump's tried so hard to stop people from getting to the border. This is the result," Raices said on Twitter.

"How many more will die before we stop criminalising newcomers and instead treat them with humanity?" the organisation said.

Trump declared a national emergency at the US-Mexico border in February, describing the irregular migration as a "growing security crisis".

