The suspected driver of a truck packed with dozens of migrants who died in sweltering heat during a smuggling attempt in Texas and an accused conspirator have been charged with human-trafficking offences.

If convicted each man faces a maximum sentence of life in prison, or possibly the death penalty, the US Justice Department said in announcing charges stemming from the deadliest migrant-trafficking incident on record in the United States.

The death toll from the tragedy rose to 53 on Wednesday as local authorities reported two more migrants initially hospitalised from their ordeal packed inside a sweltering tractor-trailer truck had died.

The truck, carrying migrants from Mexico, Guatemala, Honduras and El Salvador, was discovered abandoned on Monday in a desolate, industrial area near a highway on the outskirts of San Antonio, Texas, about 250 kilometres north of the US-Mexico border.

Temperatures in the area that day had soared as high as 39.4C, and authorities called to the scene found no water supplies or signs of working air-conditioning inside the cargo trailer.

Officials described finding the rear door to the trailer ajar with “stacks of bodies” inside, many of them hot to the touch.

Other victims were discovered on the ground nearby, some dead, some incapacitated. It was not made clear from official accounts how the door opened.

The truck’s alleged driver, Homero Zamorano Jr, 45, a Texas native who was arrested near the scene, was charged with one count of alien smuggling resulting in death, according to the Justice Department.

Police found Zamorano hiding in the bush, according to federal prosecutors.

Francisco Garduno, head of Mexico’s National Migration Institute, told a news conference earlier on Wednesday the driver had “tried to pass himself off as one of the survivors” when he was detained.

A second suspect, Christian Martinez, 28, was arrested on Tuesday and charged with a single count of conspiracy to transport illegal aliens.

His nationality was not immediately revealed.

Federal prosecutors said Martinez was linked to the ill-fated smuggling operation through communications with Zamorano detected between the two men after a search by investigators of Zamorano’s mobile phone.

Two more men suspected of involvement in the deadly smuggling incident, both of them Mexican nationals, were charged on Tuesday in US federal court with being illegal immigrants in possession of firearms.

Authorities said Juan Francisco D’Luna-Bilbao and Juan Claudio D’Luna-Mendez were arrested when they were seen leaving a San Antonio residence listed on the Texas state vehicle registration of the tractor-trailer.

Mexicans accounted for about half of those who perished. Eleven people – including minors – remain hospitalised.

As well as 27 Mexicans, the victims included 14 Hondurans, seven Guatemalans and two Salvadorans, Mexico’s government said. The nationality of some migrants remained unclear.

Most of the victims were male, with 13 females among the dead.