Distressing video footage shows more than 4,000 chickens being thrown into a pit and drowned or buried alive after they were smuggled into Thailand.

Angry locals filmed the birds being cruelly slaughtered by staff at the Songkhla Animal Quarantine Station in Hat Yai District.

The chickens had been seised by customs the day before after they were caught being smuggled into the country in trucks from neighbouring Malaysia.

The footage shows the birds struggling to breathe as they are thrown into a muddy waterlogged pit and left to drown.

Any that were still alive were then covered in soil and buried alive.

The chickens had been seised by customs the day before after they were caught being smuggled into the country in trucks from neighbouring Malaysia.

Sorawit Raneeto, the director of the Department of Livestock Development, insisted the chickens had been diagnosed with contagious diseases and were slaughtered in 'the proper way'.

Despite the footage clearly showing the birds suffering, Mr Raneeto claimed they had been stunned first before having their necks snapped.

He said: 'The officers had to quickly pull the chickens' necks to paralyse them first before they throw them into the pit, but it appeared to be alive because some of them did not die instantly.

'The chickens were diagnosed with contagious disease so we had to eliminate them as soon as possible and this is the proper way according to the chicken euthanasia.'

The footage was filmed on November 20, the day after the chickens were seised.

Officials said it took several hours to kill them all.

According to Thailand's Animal Epidemics Act, illegally smuggled chickens must be destroyed to prevent the spread of disease, particularly avian influenza, or bird flu.

But the law also states they must be killed humanely.

Angry locals filmed the birds being cruelly slaughtered by staff at the Songkhla Animal Quarantine Station in Hat Yai District.

The footage shows the birds struggling to breathe as they are thrown into a muddy waterlogged pit and left to drown.