I am a part-time staff working less than 18 hours a week. Am I protected by the MPF system?

If you are a regular employee and are employed for a continuous period of 60 calendar days or more under your employment contract, you are covered by the MPF system regardless of your working hours, full-time or Part-time. Your employer is required to enroll you in an MPF scheme.
If you are a casual employee, MPF arrangement is required regardless the length of employment, even if it is just one day, your employer still need to make contribution for you.