The HKeToll system, which requires drivers to attach a tag to their vehicles to be identified and billed, was launched at the Sha Tin control area at 5am. Drivers no longer need to stop at booths to pay when using the tunnel connecting Sha Tin and Tsuen Wan.

Before the HKeToll system was implemented, the tunnel was closed for 30 minutes from 4.30 to 5am yesterday.

Despite a signboard at the toll plaza indicated "No stopping," some drivers were still unsure. There was also some confusion as the tunnel was reduced to three lanes from seven.

Commissioner for Transport Rosanna Law Shuk-pui supervised the tunnel during the initiation. She thanked the officers from various departments for their hard work.

Authorities said that the accuracy rate of the sensors was up to 92 percent after the Transport Department tested 13 taxi drivers at Tsing Sha - the first tunnel to use the system since May 7.

But at the Shing Mun Tunnel, some taxi drivers found their vehicle tags were still undetected. A cabbie named Tsang said: "[My tag] was being detected when I crossed Shing Mun Tunnel this morning, but it failed to detect mine when I crossed the tunnel again just now."

Following the Shing Mun Tunnel, the Lion Rock Tunnel connecting Kowloon Tong and Sha Tin will be commencing on Sunday, making it the third government tunnel to adopt the system.

Authorities said that they had issued more than 720,000 HKeToll vehicle tags, covering 89 percent of Hong Kong vehicles. Among drivers who obtained a vehicle tag, 76 percent of them have registered at HKeToll.

Those without a tag will receive a reminder to pay - either by credit card, via the Faster Payment System or by cash at 7-Eleven stores - within 14 working days, with an added surcharge of HK$175 for further delay.