The Civil Aid Service (CAS) is a government auxiliary emergency service established under the Civil Aid Service Ordinance. It has an establishment of 3 634 adult members, 3 232 cadets and 111 civil servants.

Its primary duty is to provide auxiliary supporting services during emergencies. Members are trained to carry out life-saving tasks during typhoons, floods and landslips. They are taught how to combat hill fires and contain and clean up oil spills. In 2006, the CAS was called out to help rescue victims of a serious flood. Its members also carried out 60 mountain search and rescue operations, and took part in fighting 18 hill and bush fires.

On November 1, 2006, the CAS joined the Fire Services Department and Agriculture, Fisheries and Conservation Department to combat a huge fire at Tai Lam Country Park. The blaze lasted for 64 hours, razing more than 66 000 trees across 630 hectares of park land. Working in shifts, CAS personnel fought the blaze continuously for three days.

CAS personnel also patrol hiking trails and country parks on Sundays and public holidays when a lot of people make outdoor excursions. The CAS is on standby during the dry season because of the high risk of hill fires. Crowd control is included in the CAS ambit. In 2006, the CAS took part in controlling crowds at 180 public events, and stationed 35 members each day at the Lo Wu Border Control Point to help control the large crowds crossing the boundary.

The CAS also takes part in promoting civic awareness among young people and helps them develop leadership skills. It runs a CAS Cadet Corps for youths between the ages of 12 and 17. Besides participating in recreational activities, these cadets are taught life-saving techniques, rock-climbing and industrial skills such as printing, book-binding and fibreglass moulding. Cadets above the age of 13 are encouraged to perform crowd control duties and to patrol country parks.