More than 100 people - mostly from the mainland - were arrested yesterday in one of the biggest swoops ever mounted against illegal workers. A total of 57 premises in the New Territories were raided by staff from the Immigration Department and police in an operation codenamed Champion, which started at 9am. Identity checks were conducted on 342 people at container depots, recycling factories, warehouses, garages, construction sites and restaurants. Fifty Immigration Department officers and 170 police were deployed during the operation, which ended at 5pm. The Immigration Department said 104 people were arrested, aged between 17 and 58, including two employers suspected of hiring illegal workers. Of those arrested, 88 were from the mainland and the others from Pakistan, Sri Lanka, Nigeria and Nepal. A spokesman for the Immigration Department said that all of the illegal workers arrested had been hired on a casual basis. He said six men and one woman were working illegally in a plastic-bottle recycling factory for $100 to $150 a day. He said the crackdown was one of the biggest such operations ever mounted in Hong Kong and he expected more raids would be conducted. 'By carrying out these operations, we hope to protect the employment opportunities of Hong Kong people,' the spokesman said. Immigration Department figures showed that a total of 7,621 illegal workers were arrested in the first six months of this year. Of those, 5,133 were working as prostitutes. Last year 16,548 illegal workers were netted, including 11,231 working as prostitutes. The maximum penalty for working in Hong Kong without a proper permit is a $50,000 fine and two years' imprisonment, the department warned.