Britain has voted to leave the European Union in an historic referendum on Thursday.

The result, which came in at 52 per cent to leave and 48 per cent to remain, has led to an announcement by UK Prime Minister David Cameron that he will step down by October to allow for "fresh leadership".

"I will do everything I can as Prime Minister to steady the ship over the coming weeks and months, but I do not think it would be right for me to try to be the captain that steers our country to its next destination," he said, speaking outside 10 Downing Street on Friday morning.

The result, which is expected to take two years to implement, has seen the British pound fall to its lowest level against the US dollar in 31 years.

More than 33 million people took part in Thursday's vote - with the 72 per cent turnout reportedly the highest level to vote in a UK election since 1992.

The UK's Opposition Leader and Labour leader Jeremy Corbyn called for Article 50 of the EU Treaty - which sets out how a state can exit the bloc - to now be invoked.

UKIP leader, and a vocal supporter of the leave campaign, Nigel Farage, said 23rd June should now be known as the UK's "Independence Day".

Australia's Prime Minister Malcolm Turnbull has described the decision as "momentous and historic". He said while he recognised Australians would be concerned by the "uncertainly and instability" in global markets, it was "important to remember that the Australian economy is strong and resilient and has weathered global shocks before and weathered them well."