Vietnamese authorities have buried thousands of seized cats – many believed to have been alive at the time – that were smuggled from China to feed the illegal cat meat trade.

A truck carrying three tons of live cats crammed into bamboo crates was impounded in the Vietnamese capital, Hanoi, on Tuesday. On Wednesday a police officer said they had been buried in accordance with Vietnamese law on smuggled goods.

“The cats were from China, with no official origin papers and no quarantine,” said the policeman from the Dong Da district environmental police. “Several of them had died, there was a terrible smell that could affect the environment and carried risks of future diseases. Therefore, we culled them by burying them.” He declined to say how many were alive at the time of burial.

Other smuggled animals, including chickens, are routinely disposed of in a similar way.

The Asian Canine Protection Alliance, a regional coalition of animal rights groups, said it had heard “inhumane stories as to how the [cats] may have been destroyed”, and called for the practice to be stopped.

Prof Dang Huy Huynh, chair of Vietnam’s Zoology Association, said the cull was necessary to prevent the spread of disease and deter future smuggling. “The best way to cull the illegally imported animals is burning them. But this might cost more, so authorities may choose to bury them alive, still complying with procedures in accordance with laws,” he said.

Vietnamese authorities could also have checked all the animals individually for disease before deciding whether to cull them, he said. Either way, “we do not want these animals to be on the dining table at restaurants”, he added.

Cat meat, known locally as “little tiger”, is a delicacy in Vietnam and, although officially banned, it is widely available in specialist restaurants. Vietnam has long banned its consumption in an effort to encourage cat ownership and to help keep the rat population under control.

It is rare to see cats roaming the streets as most owners keep them indoors or tied up, fearing they could be stolen. Such is the demand from restaurants that cats are sometimes smuggled across the border from China, Thailand and Laos.

Vietnamese customs officials routinely seize large volumes of dead animals, including tigers and pangolins, smuggled into the country for use in traditional medicine or speciality dishes.