Up to a thousand people gathered in Tokyo on 1 July to watch a "leap second" added to their day.
The additional second was added to world clocks at midnight GMT, which was 9:00am in Japan. Crowds gathered in the capital to see a clock display the extra second, as the clock counted up 61 seconds before changing to 9am.
The decision to add a leap second had been taken by the International Telecommunication Union to allow timekeepers of high-precision atomic clocks to sync time with Earth's slowing rotation.
Earth's rotational speed has been slowing down due to the moon's gravity, causing a leap second to be added, much like the leap day added to February once in four years.
Leap seconds were introduced in 1972, by which time atomic clocks were ahead by 10 seconds. Scientists had to add 10 seconds to the world's astronomical clocks in one go back then. Since then leap seconds have been added on 25 occasions.
The last leap second was added in 2012. Then, similar to the Y2K millennium problems, a few websites were affected. Australia's Qantas Airways was among those hit as the leap second affected its reservation systems and caused flight delays.