Three live bullets, about 15cm long, and 28 spent cartridges, believed to have been used in a 'big, heavy gun' in a gunboat, were found outside a vegetable stall in Cheung Sha Wan Wholesale Food Market yesterday. Police said the ammunition was probably abandoned by a mainland illegal immigrant fleeing a crackdown on illegal workers in the adjacent Wholesale Fish Market in Yen Chow Street West. In the joint operation involving the Police Tactical Unit and Immigration Department, officers arrested 21 people at the fish market between midnight and 8am yesterday. Two of those arrested were boat captains suspected of aiding and abetting illegal immigrants. The others were 17 mainland illegal immigrants and two other mainlanders. Six grams of cocaine was found on one of the illegal immigrants. Police said they suspected the mainlanders had been hired to unload fish from boats at the market. Those arrested were detained for questioning. The ammunition was discovered by a 64-year-old cleaner at about 10am, two hours after the end of the crackdown. Police said the worker, surnamed Chan, was removing rubbish with a broom when he found the ammunition. 'The bullets were just scattered on the floor, without wrapping,' Mr Chan said. Police cordoned off the area as officers searched rubbish and bamboo baskets in the area, but no more ammunition was found. Bomb disposal officers were called in to remove the ammunition and the area was reopened at about 2pm. An officer said the ammunition appeared to be all the same type, and police were investigating where it came from. 'It is possible that a mainland illegal immigrant dumped the bullets while escaping arrest,' he said. He said it was not known whether the owner of the ammunition was among those arrested. Police are trying to get fingerprints from the ammunition in an attempt to find the owner.