POLICE have arrested eight people and questioned almost 3,000 in an eight-hour blitz on Christmas crime on Hong Kong Island. The operation is part of the annual police offensive against crime during the two-month long festive season. One reason for the ''pre-emptive step'' is to prevent gangs of robbers and pickpockets from operating over Christmas and the Lunar New Year. Seven men and a woman were arrested during the first stage of this year's crackdown which took place between 6 pm on Friday and 2 am yesterday. ''During the operation,'' a police spokesman said, ''officers from Hong Kong Island visited 153 premises and questioned 2,967 persons. The spokesman added: ''An increased police presence on the streets will enhance anti-crime efforts and ensure public order. ''The public will notice the significant increase in manpower in street patrols.''