A TEN-MAN gang armed with a gun and other weapons was arrested following a struggle with detectives inside a Kwun Tong factory building late last night. ''There are casualties on both sides, but all the injuries were minor,'' said Senior Superintendent Albert Kwok Cho-kuen of the Organised Crime and Triad Bureau early today. He said a loaded China-made nine-millimetre pistol, knives, pliers and screwdrivers were seized after the gang was subdued. He said the group - all Hongkong residents except for one who is believed to be an illegal immigrant - aged between 29 and 37, was being detained for further investigations. Police believe the gang may be linked to a series of recent robberies of companies in industrial buildings. Superintendent Kwok said his officers had been keeping the Hoi Bun Industrial Building in Wing Yip Street under surveillance after receiving a tip-off that ''something'' was to happen there. Officers spotted the suspected gang members as they began to arrive separately at the building from 8 pm. At 10 pm, they tied up and gagged all four watchmen. Detectives swooped on the gang in the building's car park as members moved in for the first robbery and a struggle erupted.