Eight people have been found dead inside a trailer truck in the US state of Texas.

Some 20 others were discovered in a critical or serious condition after suffering heatstroke or dehydration.

They have been taken to seven hospitals in the local area.

The truck was parked outside a Walmart store in San Antonio. The air-conditioning in the vehicle was not working.

The discovery was made after one of the people in the truck approached a Walmart worker and asked for water, who then called the police.

Police say they are investigating a possible people-smuggling offence.

A man who was driving the truck has been arrested.

Police Chief William McManus says: "We're looking at a human trafficking crime here... Right now we're looking at eight dead.

"There appears to be some juveniles, some adults in their 20 and 30s".

Fire Chief Charles Hood adds: "These people were in that trailer without any signs of any type of water.

"We're very fortunate that there weren't 38 of these people that were all locked inside that vehicle dead."

Authorities are trying to piece together where the trailer originated.

It is thought some of the people from the truck may have absconded before police arrived.