UK casts doubt on points-based immigration after Brexit
British Prime Minister Theresa May. (AFP)

British Prime Minister Theresa May has committed to cracking down on immigration from the European Union, while casting doubts on introducing a points-based system, according to her comments released on Sunday.

May's plans for immigration policy in the wake of Britain's decision to leave the EU remained a key discussion point as she travelled to the eastern Chinese city of Hangzhou to attend the G20 summit.

"They (voters) wanted to see an ability to be able to control the movement of people from the European Union. And obviously that's what I say, not free movement as it has been in the past," she told journalists on Saturday.

The June 23 referendum saw Britain vote by 52 percent to leave the EU, following a campaign which was dominated by immigration.

May was appointed after her predecessor David Cameron resigned following the vote and -- although she campaigned to remain in the EU -- she has promised to forge ahead with Brexit.

Since the result, the new government has grappled with how Britain could restrict migration from the remaining 27 EU nations, and thus violate a core EU principle, without losing access to the bloc's single market.

Foreign Minister Boris Johnson -- one of the leaders of the Brexit campaign -- has said such a combination can be achieved with a points-based immigration system similar to the Australian model.

But May cast doubt on such an approach, while recalling her expertise as Britain's former interior minister.

"One of the issues is whether or not points-based systems do work but what I'm saying is, the British people... didn't want the free movement to continue as it has in the past. We will be going out there to deliver on that," she said.

-'Historic and positive moment'-

During the discussion en-route to China, May said she did not want to "give away any sort of part of our negotiating hand" ahead of formal talks with the EU.

She said there was no "single silver bullet" which could provide an answer to dealing with immigration.

"You have to look across the board, you have to look at the whole range of issues.

"And obviously dealing with people if they're discovered here illegally," the prime minister said.

May reiterated that there would be no change in the status of EU citizens currently living in the UK before Britain leaves the bloc, which would follow two years of negotiations sparked by the government triggering the Article 50 mechanism.

"I expect to be able to guarantee their status. The only circumstances in which that wouldn't be possible, is if other EU countries don't guarantee the status of British citizens who are living in other EU countries," she said.

The prime minister has repeatedly expressed her intentions to be ambitious in EU negotiations, adopting an upbeat tone echoed by Brexit minister David Davis.

"This is an historic and positive moment for our nation. Brexit isn't about making the best of a bad job. It is about seizing the huge and exciting opportunities that will flow from a new place for Britain in the world.

"There will be new freedoms, new opportunities, new horizons for this great country," he said in a statement.

Davis is expected to make a statement in parliament on Monday, the details of which have not been published.