Sales of smartphones will continue to grow over the next four years, according to a new study by technology analysis firm IDC.

In total, shipments will rise by 16 per cent between now and 2021 to 1.7 billion IDC predicts.

This is despite an apparent slowdown in sales last year, with sales of such devices rising just 2.5 per cent - the first year that sales only increased by single digits.

But IDC thinks that new demand from users and a consistent replacement cycle will boost average annual sales to 3.3 per cent.

IDC says around half of the world's population now has a smartphone, which means there's plenty of opportunity for growth.

It also predicts that most existing smartphone users will continue to update their handsets around every two years.

Google's Android will continue to dominate the global operating system market it says, with modest growth of around 2.3 per cent expected this year.

Apple will remain in second position with a continuation of the 14-15 per cent market share it currently enjoys.

iOS use is expected to grow about 1.5 per cent this year, with a more significant boost to follow once the iPhone 8 is launched.

However, IDC believes Apple will own 36 per cent of the device market value by 2021 - more than half of the combined value of all other Android devices.