Hong Kong immigration authorities arranged a chartered flight to send 68 unsuccessful asylum seekers and illegal immigrants back to Vietnam on Thursday in a new bid to tackle the huge backlog of cases involving torture claimants in the city. The move was expected to boost efficiency if adopted as common practice, as it would mean bigger groups being deported in one go. Before this, only a few people were flown out on regular flights each time. Immigration officers are deployed as escorts on some trips. On Thursday, 30 men and 38 women were flown back on a Vietnam Airlines flight which arrived in Hanoi at 5.15pm. Except for three infants under two years old, the other 65 people were aged between 18 and 64. Their average stay in Hong Kong was 10 months. Half of them sought asylum but were unsuccessful. Watch: failed asylum seekers sent back on chartered flight (video provided by the Immigration Department) The Immigration Department said the illegal immigrants were returned to Vietnam on a voluntary basis. On Friday, William Fung Pak-ho, assistant director of the department, said the idea of the chartered flight arrangement had long existed, but realising it had been difficult. “We have to settle their ID documents, coordinate with the Vietnamese government on receiving them and address safety concerns raised by airline operators,” Fung said. He said authorities would in future also consider chartering flights to send back illegal immigrants who were unwilling to leave. According to Fung, reviews of Thursday’s operation were submitted to the Department of Justice. Treat us as human beings, plead asylum seekers in Hong Kong “We conducted seven deportation operations this year. Some people resisted at the airport and it took two or three attempts to successfully send them back,” Fung said. “Some even screamed on flights, resulting in the airlines offloading them.” The issue surfaced almost two years ago, with the city facing a mounting number of migrants claiming refugee status and asylum. At the height of the trend, not including incidents from mainland China, the department saw about 480 new cases a month in the second half of 2015, compared with an average of 120 cases monthly between 2010 and 2013. Out of these, people from Vietnam formed the largest number of non-refoulement claimants and illegal immigrants in Hong Kong. From 2014 to November this year, official statistics showed that 3,913 of 15,268 claims made – or 26 per cent of the total – were from Vietnamese. Over the same period, 5,104 of the 8,861 illegal immigrants coming into the city were Vietnamese, accounting for 57.6 per cent of the total number. Explainer: how Hong Kong has for decades been a migrant magnet In all, 5,053 new applications were submitted to immigration officers in 2015, resulting in a backlog of 10,922 cases that year waiting to be screened. The influx prompted then chief executive Leung Chun-ying to consider withdrawing the city from the UN Convention Against Torture. Under the convention, Hong Kong has a legal obligation not to send back refugees at risk of torture or persecution in their home countries. In his January 2016 policy address , Leung also announced a wholesale review of the current system. As of November this year, authorities had processed 15,259 cases and substantiated 85 of them. Claimants whose cases are substantiated are referred to the UN for resettlement in a third country. Hong Kong does not resettle asylum seekers as it is not a signatory to the UN Refugee Convention.