Japanese police suspect involvement of a group of Vietnamese behind the disappearance of hundreds of pigs and chickens, as well as thousands of pears and peaches, from farms this year in eastern Japan.

In connection with a series of suspected thefts of livestock and fruits in the northern Kanto region near Tokyo, nearly 20 Vietnamese have been arrested on suspicion of overstaying their visas or slaughtering pigs at home without permission from authorities, according to the police.

Four male Vietnamese technical trainees aged between 20 and 30 were arrested last month for allegedly cutting pigs into pieces at their apartment in Ota, Gunma Prefecture, around July.

After receiving reports that meat and fruits were illegally traded on social media, local police have confiscated frozen pork, knives and other tools from the apartment and said video footage from one of the trainees' social networking accounts shows a piglet being grilled over flames.

"I purchased pigs by social media," the police quoted one of the four suspects as saying.

People in Japan are required to slaughter livestock in an authorized slaughterhouse, unless they obtain permission from a prefectural government.

Gunma prefectural police also arrested a group of 13 Vietnamese men and women in late October on suspicion of overstaying their visas, suspecting several of them were behind the thefts of livestock and fruits. About 30 frozen chickens were found during a house raid in Ota, the police said.