Police in Shandong province are investigating a wealthy businessman who allegedly punched a flight attendant and had his assistants beat up a policeman after being asked to show his boarding pass. Wang Tingjiang , boss of the Huasheng Jiangquan Group, allegedly punched a steward on Saturday during a stopover in Linyi, while flying from Guangzhou to Qingdao . Policeman Zhang Qiang handcuffed himself to Wang to prevent further violence, newspaper reports said. But one of Wang's assistants made a telephone call and a gang of a dozen young people then stormed into the restricted area at the airport and boarded the aircraft, witnesses said. The gang dragged the officer from the plane after unlocking the handcuffs and beat him until he could no longer stand, reports said. 'A female staff member in charge of security inspections had her fingers cut trying to close the door to prevent the gang from breaking into the airport's controlled area,' an airport official said. Sources in Linyi say Mr Wang is a powerful figure and a Shandong representative to the National People's Congress. Police yesterday would not say whether they had taken anyone into custody, but confirmed that an investigation was under way. Hao Jie , a deputy director of the airline police based in Shandong, said Officer Zhang was later taken to hospital in Qingdao with eye injuries but was in a stable condition. The flight attendant was distressed but not physically injured. 'It was a severe attack and the people responsible for this are absolutely lawless,' Mr Hao said. 'It's very rare for people to break into the airport's controlled area because the entry and exit points are subject to strict safety restrictions.'