New Zealand's population continues to grow older, with the median age increasing by more than two years in the last decade, figures released by Statistics New Zealand today show.

As of December, the median age was 36.7 years old, an increase of 2.2 years compared a decade ago, Statistics New Zealand said.

Meanwhile, in the year to December, the country's estimated population grew by 1.1 per cent to 4,393,500.

The population rise was due to a natural increase (more births than deaths) of 35,800 and net migration of 10,500.

The increase was less than the average annual increase of 1.3 per cent over the past decade.