Police are investigating efforts by a gang to extort money from drivers of red-topped Kwun Tong minibuses. The probe follows an incident in which about five suspected gang members smashed the windscreens and windows of eight minibuses parked on Hip Wo Street, Kwun Tong, at 3am yesterday. Some drivers said they were approached by suspected gangsters there last month and threatened with violence if they continued to drive their route between Kwun Tong and Yau Tong districts. 'The drivers were allegedly told they would have to stop driving or they would face violence or assault,' a police investigator said. 'It appears to be classic extortion. We are still investigating whether there is a triad that is trying to strengthen its influence in the district.' A police spokeswoman said yesterday the gang escaped in a taxi, abandoning five hammers and four pairs of gloves at the scene after vandalising the minibuses. Police mounted a search but no one was arrested. Anti-triad officers from the Kowloon East regional crime unit are investigating whether the reported intimidation and yesterday's attack were linked. The minibus route between Kwun Tong and Yau Tong has been operated by more than 10 drivers for several years. Red minibus drivers set their own routes and fares, while green minibuses are run by companies and regulated by the government. Police have broken up several gangs that demanded 'admission charges' and 'monthly fees' from drivers of red minibuses in recent years. In 2000, officers broke up a 14K triad gang that was demanding a $30,000 'admission fee' and monthly protection money from minibuses running between Wan Chai and Mongkok.