Rail workers in Texas found six people dead inside a boxcar at a yard close to the Mexican border on Sunday afternoon, officials said.

The discovery was made by a Union Pacific employee inspecting the stopped train at the yard in Laredo before it continued its journey north, a spokesperson for the Laredo police department said, citing the railroad freight company.

Authorities are working to establish a cause of death for the six, who were found at about 2.30pm local time on an afternoon when temperatures climbed above 90F (32C). Nobody was found alive in the boxcar, the spokesperson said.

“It’s a very unfortunate event. It was too many lives that were lost,” Jose Espinoza, the department’s public information officer, told CNN, adding that the ages and immigration status of the deceased were not yet known

The investigation, he said, was at a preliminary stage.

US Customs and Border Protection (CBP) said it was aware of the incident, and referred questions to the Laredo police department and Texas Rangers.

Sunday’s discovery has parallels in a 2024 episode in which 20 migrants locked inside a train compartment in Laredo were rescued in a dehydrated state by CBP officers.

The Laredo Morning Times reported in 2024 that Laredo was the busiest port for international trade in the country, with an average of 12 trains per day entering from Mexico, bringing in almost 1,500 loaded containers between them.

Union Pacific, one of the largest rail operators in the US, operates many of the trains, and said it was cooperating with authorities after the deaths on Sunday.

“Union Pacific is saddened by this incident and is working closely with law enforcement to investigate,” Daryl Bjoraas, a spokesperson for the company, said in a statement.

The Trump administration has clamped down on illegal immigration at the Texas-Mexico border, but its claim that crossings have dropped to zero has been challenged in recent days. Axios reported that the CBP’s own figures said 8,000 people were apprehended trying to cross in March, a 15% increase on 2025.

Meanwhile, plans are reportedly advancing to close a controversial border immigration jail sited at the Fort Bliss military base in El Paso, about 600 miles (966km)from Laredo. At least three detainees have died in Immigration and Customs Enforcement (ICE) custody there, and in March the facility was also struck by a measles outbreak.

In 2022, 53 migrants, including six children, from Mexico, Honduras, Guatemala and El Salvador were found suffocated to death inside a locked tractor trailer with no air conditioning or water, having been packed into the vehicle in Laredo for a journey to Forth Worth, Texas.

Two of the men who abandoned them, Felipe Orduna-Torres and Armando Gonzales-Garcia, were sentenced to life imprisonment last year, while five others faced smuggling charges.