Police are investigating if a man ferrying 10 Myanmar nationals in a tinted car that was involved in an accident at Km134.1 of the East Coast Expressway on Monday, was involved in human trafficking.

Temerloh District Police chief ASP Mohd Annuar Othman said investigation was being carried out from various angles to determine if the suspect, who had a record for theft in 2003, operated alone or with a syndicate.

"The suspect, 29, who was also the driver of the car, a Honda Accord, is still unconscious. He is being treated at the Sultan Ahmad Shah Hospital here and will be interrogated as soon as he regain conscious," he told a media conference at the Temerloh District Police Headquarters here on Monday.

In the 4.30am incident, four were killed after they were thrown out of the car while seven others, including the driver, were injured after the Honda Accord skidded into a drain and overturned, near here.

He said it was difficult to determine the identities of the Myanmar nationals, in their 20s and 30s, as no identification documents were found and police believe they are illegal immigrants.

The car, which was driven by Che Mohd Azuwan Che Hashim, 29, of Tanah Merah, Kelantan with 10 Myanmar nationals, was believed to have left Rantau Panjang, Kelantan for Kuala Lumpur at 6.30pm on Sunday.

He said four of the seven injured were discharged and had been detained at 5pm to facilitate investigations while three were still warded, including Che Mohd Azuwan.