Authorities have foiled two suspected animal smugglers allegedly selling wild monkeys to China to be eaten and have their brains used in medicine.

Thai Highway Police arrested Pongpat Sooksom, 32, and Phutanate Puttawong, 21, while they were delivering dozens of crab-eating macaques to Bueng Kan province in Thailand's far northeast bordering Laos, on Tuesday June 6.

The pair were detained along Highway 2096 in the Nong Han district of Udon Thani province after officers received a tip-off from the Natural Resources and Environmental Crime Suppression Division.

Inside the suspects' white Chevrolet were 27 monkeys mercilessly stuffed in blue mesh bags. One of the animals had died in transit.

The rescued macaques were taken to a wildlife centre in Khon Kaen, while the alleged traffickers were handed over to the Nong Han District Police Station for questioning.

Lieutenant Colonel Krit Srihaboontan of the Highway Police Station 3, Fourth Division said in a June 6 press conference: 'The operation was a collaborative effort among the Highway Police, the Natural Resources and Environmental Crime Suppression Division (NED), and the Department of National Parks, Wildlife and Plant Conservation (DNP).

'We learned that the crab-eating macaques had been collected from central Thailand, and were en route to an agent at the border before being smuggled to other countries.'

DNP officials said the creatures were being sold for up to 12,500 THB (360 USD) each. Because of the handsome payment, local poachers had begun hunting them at night, the agency said.

Authorities believe the monkeys' brains were being harvested for cancer and lupus vaccine research, while their meat was being consumed as exotic dishes.

Pongpat and Phutanate allegedly admitted to the smuggling and told cops they earned around 9,500 THB (273 USD) for each monkey sold, with the price increasing to 10,000 THB (287 USD) once they've reached their destination.

They reportedly said it was their third time smuggling monkeys out of Thailand.

They have been charged for unauthorised possession of wildlife and have declined to comment further.

Last April, wildlife conservation officials in the same district arrested another driver accused of smuggling dozens of macaques believed to be destined for China.

Officers from the Protected Area Region 10 Office had found 44 sedated crab-eating macaques crammed in plastic boxes inside a 'suspicious car' in Udon Thani's Nong Han district. Three of the animals had died of suffocation.