Fewer vehicles went through the busy Cross-Harbour Tunnel and Eastern Harbour Crossing and more drivers instead opted for the quieter Western Harbour Crossing on Monday after new time-varying tolls came into force, the government says.

The tunnels' fees now vary depending on the time of day, with higher tolls during peak hours. The change means significantly cheaper tolls for the Western Harbour Crossing in quiet periods, down to as little as HK$20, compared to the previous HK$60 all-day charge.

Transport Commissioner Angela Lee said this tunnel saw a 14 percent increase in traffic on Monday, while traffic was reduced at the Cross-Harbour Tunnel by 14 percent, and at the Eastern Harbour Crossing by 9 percent.

"During rush hours, the queues at the Cross-Harbour Tunnel and Eastern Harbour Crossing were shorter, as we expected. The queues were around 0.5 to one kilometre shorter than usual," Lee said.

"We observed there were often queues at the Cross-Harbour Tunnel outside of the peak hours in the past, but on that day we couldn't really see vehicles lining up."

Lee said the authorities will continue to monitor changes in commuting patterns, noting that school and public holidays may have an effect on the usage of the tunnels.

Meanwhile, officials announced that the Aberdeen Tunnel will be closed for an hour from 4am on December 24, ahead of the 5am launch of HKeToll there.

From Sunday, the privately-owned Tai Lam Tunnel will be the only tunnel in the city not using the e-toll system.