Jewellery and watch shops are being warned about a suspected professional thief who stole a $150,000 diamond necklace from a Tsim Sha Tsui shop yesterday afternoon. The smartly dressed man duped a saleswoman by paying her a 2,000 yuan deposit and handing her the jewel case for wrapping. He then stepped out of the store, saying he was going to get the balance of the cash. The 23-year-old saleswoman did not realise until he had gone that the man had already removed the necklace from the case. Police said they suspected the man had come from the mainland, looking for easy opportunities to steal. The man went into the jewellery shop about 2pm. 'He paid 2,000 yuan to the saleswoman and then asked her to wrap it, claiming that he would return later and pay the outstanding balance,' a police officer said. After he left, the saleswoman opened the case and found the necklace was missing. The man, thought to be about 40 years old, was of thin build and had short hair. He was wearing a dark suit. A police source said his ruse was a common trick used by professional thieves. A number of similar thefts have been reported in Tsim Sha Tsui in the past two years, including that of a $100,000 watch.