HONG KONG • A man has reported the loss of HK$2 million (S$346,000) worth of foreign currency and valuables on board a Hong Kong-bound plane, in what is believed to be the biggest in-flight theft in the city.

The passenger, a 39-year-old expatriate travelling on an Emirates flight from Dubai yesterday, realised his loss only after he had stepped off the plane at Hong Kong International Airport, the South China Morning Post reported. The money and valuables were in the man's bag, which was stowed in an overhead cabin during the flight, the Post said.

The man sought help from airline staff, who called the police at about 6am. "Initial investigation showed two watches and over US$200,000 (S$268,000) were stolen from his bag and the total value was about HK$2 million," a source with knowledge of the investigation was quoted by the daily as saying.

The police are treating the case as theft and are investigating. So far, no one has been arrested.

The source said it could be the costliest case of in-flight theft in recent years as most reported losses in the past were valued at hundreds of thousands of Hong Kong dollars, not millions.

An Emirates staff member surnamed Kwok who answered the airline's hotline yesterday declined to tell the Post whether it was the carrier's first reported in-flight theft for a Hong Kong-bound flight.

The Hong Kong authorities have seen an increase in in-flight thefts, the Post said. In the first 10 months of last year, there were 67 reports of thefts on flights bound for Hong Kong, with the loss of a combined HK$4.83 million, the report said. At least one-third of the cases were discovered by flight attendants. That compared with 48 cases and HK$2.61 million in losses for the whole of 2014, according to the report.

Another source was cited as saying the criminals often posed as well-dressed travellers and preferred aisle seats. "They scouted their prey before boarding and placed their own bags in the same overhead bins their targets used."