The system is mandatory for all employees in Hong Kong who have an employment contract of 60 days or more and applies also to the self-employed between ages 18 and 65. Those employed in the catering and construction sectors are generally exempt but they may be covered on a daily basis. Hawkers (street vendors), domestic employees, persons covered by statutory pension or provident fund schemes such as civil servants or teachers. Members of occupational retirement schemes with specific exemptions, and foreign citizens who work in Hong Kong for periods shorter than 13 months or who are covered by another country's retirement system may also be exempt.