Lawmakers on Wednesday started debating a bill that would change tolls for Hong Kong's three harbour tunnels, as officials retake control of the Western Harbour Crossing.

The government plans to bring in the new charges on August 2. Tolls for private cars will go up at the Cross-Harbour Tunnel and Eastern Harbour Crossing, from HK$20 and HK$25 respectively to HK$30.

Fees for the Western Harbour Crossing, meanwhile, will be reduced from HK$75 to HK$60.

Later in the year, the government is also looking to implement a new time-based tunnel fee structure, that will see motorists pay up to HK$40 if they use the Cross-Harbour and Eastern Harbour crossings during rush hours.

DAB lawmaker Chan Hok-fung said he believes the time-variant toll arrangement can alleviate a long-standing congestion problem.

"With time-variant tolls, motorists would get a choice. They can pick the right time for them to cross the harbour, they get to save money, then you can get efficiency,” he said.

However, independent Kitson Yang said he thinks a fourth tunnel is needed to resolve the traffic jam problem.

Transport sector lawmaker Frankie Yick from the Liberal Party, meanwhile, moved an amendment aimed at lowering the tunnel fees for taxis and commercial vehicles.

He said while he supports the toll changes in general, the government needs to take better care of commercial drivers.