At least 10 people were killed and another 17 injured when about 10 cars were piled up late Wednesday on a Mexico City highway after a trailer truck's brakes failed, local authorities said Thursday.

Six of the injured are in serious condition, including an infant that sustained head injuries, the city's attorney general Edmundo Garrido told reporters.

Nine people were said to be killed on the spot, with the 10th death confirmed on Thursday.

Preliminary police reports said the truck was carrying 25 tons of soap and traveling at a speed of more than 100 km per hour when the brakes failed.

Tests showed that the driver, a 41-year-old woman, was not under the influence of drugs or alcohol, said Garrido. She is currently in custody.

The crash occurred at 7:07 p.m. local time(0107 GMT Thursday) along the highway connecting Mexico City with Toluca, the capital of central Mexico State.

"They (the vehicles) were crushed like an accordion," an eyewitness told reporters at the scene.