Commissioner for Transport Rosanna Law said around 17 percent of drivers who passed through the tunnels where the government's new e-toll system came into operation on Sunday did not have a tag for automatic payment of the toll.

The HKeToll system, which lets drivers pay tolls without having to stop, was implemented at the Tsing Sha control area of the Eagle's Nest, Sha Tin Heights, and Tai Wai tunnels.

"Up until 10 am, a total of 6,178 vehicles had passed the Tsing Sha control area. We couldn't detect any vehicle tag on 1,048 of them," Law told reporters.

"I saw from media reports that drivers who had used the e-toll service felt that it was convenient, so I call on those who haven't applied for an e-toll vehicle tag to do so as soon as possible."

On Friday, Law said over 85 percent of the cars in the SAR had registered for the system. Drivers who don't have a tag will be sent a bill for their tunnel use.

The official said operation of the new service was smooth in general, although some drivers still slowed down at toll booths before tunnel workers quickly waved them through.

She said some vehicles had also used the wrong lanes, adding that the Transport Department will put up more signs to give clearer directions.

"The left most lane is for buses to get to the bus interchange, but we also saw it being used by some heavy vehicles, which are used to using the left most lane," the commissioner said. "We will try to install a new sign today, so there will be more direction for people going to work or school tomorrow."

Law said she is confident that drivers will quickly adapt to the new e-toll system.

Officials aim to extend HKeToll to all government tunnels later this year.