A robbery gang who used an innocent-looking child to stage the audacious theft of a HK$36 million diamond necklace from under the noses of staff at a luxury jewellery shop were being hunted by police last night. The heist - which detectives have described as "very well planned" - unfolded when two women, a man and a girl thought to be between 12 and 14 years old walked into the Emperor Jewellery shop in the 1881 Heritage shopping mall in Tsim Sha Tsui shortly after 3pm yesterday. Well-dressed and speaking Putonghua, the trio of adults, managed to distract staff by asking to look at a series of items on display while the girl stole a key from a drawer, opened a display cabinet then slipped the necklace off a display bust and into her pocket. The girl was was later caught on CCTV cameras calmly walking out of the mall. Detectives say she may have quickly changed her appearance after leaving the shop before jumping into a taxi to escape. Her adult accomplices, who police say are aged between 30 and 40, remained inside the mall as if nothing had happened. Shop staff did not notice the 100-carat gold necklace embedded with more than 30 diamonds was missing until shortly before 5pm. A 63-year-old member of staff then called police. "Initial investigations suggest the girl stole a key from a drawer and then opened a display cabinet to steal the necklace when the three adults - one man and two women - kept staff busy," a police source said, adding that it was the first time in recent years a child had been used in such a heist. "The necklace was embedded with more than 30 diamonds totalling about 100 carats. We were told it was worth about HK$36 million. "The three adults posed as big spenders and demanded employees show them jewellery in an apparent move to divert staff attention," the source said. Police said that after spending more than 30 minutes in the shop, the four left without buying anything. A search was mounted but no arrests were made. The girl is about 1.4 metres tall and was wearing a grey windbreaker, dark jeans and black shoes after she left the shop but may have been dressed in pink and white inside the shop. Border officers are looking out for the thieves as police believe they will flee the city. Some of Hong Kong's recent audacious heists September 2014 : A man eluded heavy security and stole a 4.8-carat diamond worth about HK$800,000 by swapping it with a fake at the Hong Kong Jewellery and Gem Fair after asking to see the merchandise. April 2014 : A robber posing as a big spender managed to convince a sales assistant to let him try on two luxury watches at the Zenith Boutique in Tsim Sha Tsui - and then bolted out the door with his HK$480,000 haul. It was a simple ploy: the 1.8-metre-tall man outran the staff members who chased after him. February 2014 : An audacious shoplifter left Burberry - one of the world's biggest designer brands - red-faced after he walked out of its Tsim Sha Tsui store with a HK$995,000 alligator skin coat. The robber - caught on security cameras - simply lifted the trench coat off the mannequin and calmly walked out. October 2013 : Two thieves poured kerosene on employees of a Diamond Collection shop in Tsim Sha Tsui and threatened them with what appeared to be a pistol, before fleeing with HK$10 million worth of diamonds in a 60-second heist. The two men were dressed as construction workers, wearing yellow safety helmets, reflective vests, face masks and gloves.