Officials said on Tuesday there will initially be five bus routes using the new Tseung Kwan O-Lam Tin Tunnel after it begins operations next month.

The new 3.8-kilometre connection and the adjacent Cross Bay Link, a 1.8-kilometre bridge, will open on December 11.

The authorities said they picked five bus routes, which will start service from December 12, for the new HK$15 billion tunnel. They added the five routes will only operate during peak hours on weekdays for now.

"There are two stages to introduce bus routes via [the] Tseung Kwan O-Lam Tin Tunnel," explained Honson Yuen, an assistant commissioner for transport.

He said these buses will travel between Tseung Kwan O and Tai Po, Cheung Sha Wan, Sham Shui Po, Tsuen Wan and the Yau Tsim Mong area.

He added that four more bus routes will use the new tunnel later.

"We'll look at the traffic situation to decide [the] exact timing to introduce the four routes going via [the] Tseung Kwan O-Lam Tin Tunnel in the second stage," said Yuen, who added that additional bus services may be available in future depending on the views of the local community and traffic situation.

The HK$5.6 billion Cross Bay Link is the first viaduct that features carriageways, bicycle tracks and footpaths in Hong Kong.

Authorities say they expect the new transport link can divert up to 40 percent of the vehicles from the current Tseung Kwan O Tunnel and cut the transport time between Tseung Kwan O and Kowloon Bay by 20 minutes during peak hours.