The audacity of mainland theft syndicates has soared sky-high - literally.
Well-dressed crooks posing as travellers are stealing valuables worth hundreds of thousands of dollars from the overhead lockers of Hong Kong-bound flights, police say.
Syndicate members rummage through travel bags and luggage stowed in the lockers when the owners are asleep or in the toilet.
'They scout their prey before boarding and place their own bags in the same overhead compartment their targets use,' a police officer said.
Last month, there were at least two such thefts involving foreign currency and diamonds worth more than HK$250,000.
On June 10, three diamonds worth US$18,000 and US$8,400 in cash were stolen from the bag of a foreign trader on a flight from Kuala Lumpur. Last Thursday, US$6,900 and Euro30 (HK$295) was stolen from the bag of a German tourist who arrived from Bangkok.
Most of the thefts took place on short-haul Hong Kong-bound flights.
Police said officers first noticed the trend towards this type of crime in August last year.
Latest figures show that there were 39 reports of in-flight theft in the first five months of this year, nearly double the 21 cases reported for the whole of last year.
But police said the figures did not include thefts that took place on outbound flights.
Police are understood to have arrested a number of mainland suspects in connection with the thefts.
'Police have closely monitored recent in-flight thefts, stepped up communication and co-operation with airlines and enhanced publicity and collection of intelligence to fight and prevent the crime,' a police spokesman said.
After receiving reports of suspected inflight thefts, officers will board aircraft to investigate and make arrests if suspects are found.
'Police have sought help from airlines, asking their cabin crew to remain vigilant on flights,' a senior police officer said.
He also appealed to travellers to keep their valuables safely secured on flights, especially during the summer holidays.
Cathay Pacific declined to disclose the number of thefts on its flights, but would notify police of any reports.
'As always, and with all issues of this nature, we work very closely with the police and support initiatives recommended by the authorities,' a spokeswoman said.
'People are always reminded of their responsibility to take care of their valuables and belongings at all times.'
Hong Kong Airlines also declined to provide the number of in-flight thefts on its flights and did not say whether police had sought help from the company.
A spokeswoman said the airline's cabin crew had been trained to watch for in-flight crime.