On Thursday, police revealed they had arrested seven men from mainland China so far this year in connection with 12 thefts that occurred while planes were in the air.
Among the most daring crimes, an Algerian man flying to the city from Turkey found that HK$45,000 (S$7,871) worth of US dollars in his wallet had been replaced by just HK$2,700 worth of Libyan dinars.
The man only discovered the theft once he had left the plane, and the thief has so far not been identified.
Meanwhile, the greatest loss involved valuables and cash worth a total of HK$55,000.
Six of the suspects, who are aged between 37 and 50 are awaiting trial, while a seventh man, who was arrested in April, was earlier found guilty and sentenced to a year in jail.
The total of 12 cases is five more than reported throughout last year, but remains much lower than the 22 and 77 cases reported in 2016 and 2015 respectively.
Switching currency was a common occurrence in this type of theft, according to detective inspector Annie Cheng Tsz-in.
"We would like to remind all passengers to keep valuable belongings close to them, put a lock on their luggage, carefully check their bags before leaving the aircraft, and seek help from the cabin crew in time," she said.
Cheng said the police had also been providing training to flight attendants to raise their awareness of suspicious people and activities on-board planes.
"At least two cases, both in November, were reported by the cabin crew, and in one of them the thief was stopped before he got to the victim's property," Cheng said.
In that case, a man was spotted by a flight attendant as he tried to force open a padlock with his own key. In the other incident, another man was caught by cabin crew as he took another passenger's bag from an overhead locker in which there was US$700 and 2,000 yuan in cash.
The maximum sentence on conviction of theft on a flight operated by airlines registered in Hong Kong is 10 years in jail. But for theft on a foreign flight to Hong Kong the maximum punishment is a HK$50,000 fine and two years in prison.
Including the 12 thefts, airport police recorded a total of 642 crimes between January and November this year, about the same level as 2017 when there were 698 cases for the year.
More than half of the crimes involved possession of restricted items, among which most involved people carrying extendable batons.
More than 60 per cent of the 154 passengers, aged between 16 and 83, arrested for keeping an extendable baton in their bags were in transit.
Of that number, more than 80 per cent of them bought the batons outside the city in places such as mainland China, the Philippines, Thailand and Indonesia.
"The extendable batons are relatively cheap and easily available in the market, therefore many people might buy it as a souvenir, or for self-defence, without knowing they are not allowed for personal possession in Hong Kong," Cheng said.
Police also arrested 138 passengers for carrying stun guns, 18 for possessing bullets, 12 with pepper spray, 10 with knuckle dusters, and three with flick knives, or butterfly knives.
"Though some restricted items might be allowed in the countries and territories a passenger came from, we will have to arrest them when it is found in the luggage," Cheng said.
"In that case, the passenger's travel plan will definitely be disrupted and legal trouble will follow."
The police have also been holding regular seminars with the aviation industry, and asking foreign consulates tell their nationals who are planning to travel to the city.