A leap second will be added to the Coordinated Universal Time at 7:59:59am on January 1, Hong Kong time.

The Hong Kong standard time, eight hours ahead, will be delayed by one second accordingly. The whole process will be completed in two seconds, at 8am Hong Kong time.

Coordinated Universal Time is the current international time scale for civil use. It is a stable and even time scale based on the frequency of atomic oscillations in atomic clocks.

The astronomical time scale based on the Earth's rotation is another common time scale. As a result of atmospheric circulation and other geophysical events on the planet, the rate of the Earth's rotation is uneven and slowing down.

One second based on the astronomical time scale is slightly longer than that on the standard atomic time scale. This means a leap second must be added from time to time to reconcile the two time scales so that the difference between them is kept to less than 0.9 second.

Leap seconds have been introduced 24 times since the adoption of the Coordinated Universal Time in 1972. The last adjustment was made on January 1, 2006.