Hong Kong police are hoping to enlist the city's army of taxi drivers in their fight against terrorists, with an initiative aimed at teaching cabbies what to do when they overhear their passengers plotting attacks.

This comes after police received some 20,000 tip-offs via a counter-terrorism WeChat and SMS hotline launched last summer. Officers looked into about one in seven of the reports.

The force said one of the first rewards paid out to informants went to a taxi driver who overhead two passengers talking about a "violent attack", which turned out to be a bomb hoax.

Senior superintendent Leung Wai-ki from the force's Inter-departmental Counter Terrorism Unit said Hong Kong's 40,000 or so taxi drivers can play an important role in fighting crime.

"Taxi drivers travel across the city every day and encounter different people and incidents. They may come in contact with crime-related information when carrying passengers or driving along the road," he told reporters.

"We will provide important counter-terrorism and anti-crime information to people in the taxi trade."

Police say taxi drivers don't need to worry about being accused of breaking the law if information they provide turns out to be false.