The death toll of deceased migrants found inside a truck in Texas has risen to 50, Mexican President Andres Manuel Lopez Obrador says, in one of the most deadly recent incidents of human smuggling along the US-Mexico border.

The deceased migrants were discovered inside a tractor-trailer on Monday in San Antonio, Texas, where temperatures swelled to a high of 39.4 degrees Celsius.

Local and US authorities said there were no signs of water and no visible working air-conditioning inside the truck.

“I want to offer my condolences to the relatives of this catastrophe,” Mr Lopez Obrador said.

Mexico Foreign Minister Marcelo Ebrard said on Twitter on Tuesday that 22 Mexicans, seven Guatemalans and two Hondurans were identified among the dead.

There was no information on the citizenship of another 19, Mexican officials said.

The US Immigration and Customs Enforcement (ICE) said that its Homeland Security Investigations division was conducting a criminal investigation into “an alleged human smuggling event” in co-ordination with local police.

Sixteen other people found inside the trailer were transported to hospitals for heat stroke and exhaustion, including four minors, but no children were among the dead, the San Antonio Fire Department said.

Mr Lopez Obrador said on Tuesday he would meet US President Joe Biden in Washington DC on July 12. Migration would be a central issue in their discussions, he said.

Earlier, a San Antonio Fire Department official said they found “stacks of bodies” and no signs of water in the truck, which was found on Monday next to railway tracks in a remote area on the city’s southern outskirts.

Sixteen other people found inside the trailer were transported to hospitals for heat stroke and exhaustion. They included four minors, although no children were among the dead, the department said.

“It’s probably close [to] 100 in the truck,” a law enforcement source told the San Antonio Express-News, adding that “about half” of the group were likely dead.

The discovery prompted an enormous police response, with first responders seen walking along the tracks with thermal imaging cameras, apparently searching for more people.

San Antonio police were also searching for the truck’s driver, who had apparently abandoned the vehicle prior to its discovery, The New York Times reported.

The I-35 highway near where the truck was found runs through San Antonio from the Mexican border and is a popular smuggling corridor, according to Jack Staton, a former senior official with ICE’s investigative unit who retired in December.

In July 2017, 10 migrants died after being transported in a tractor-trailer that was discovered by San Antonio police in a store car park.

The driver, James Matthew Bradley Jr, was sentenced the following year to life in prison for his role in the smuggling operation.

-Reuters