Britain's new Prime Minister Boris Johnson gives a speech at 10 Downing Street in London, Britain on July 24, 2019. Newly-elected Conservative Party leader Boris Johnson took office as the British prime minister on Wednesday amid the rising uncertainties of Brexit. (Photo by Alberto Pezzali/Xinhua)

LONDON, July 24 (Xinhua) -- Newly-elected Conservative Party leader Boris Johnson took office as the British prime minister on Wednesday amid the rising uncertainties of Brexit.

The latest development came after Theresa May formally stepped down as the leader of the country and Johnson was invited by the Queen to form the government.

Johnson, former British foreign secretary and ex-mayor of London, became the prime minister as Britain is faced with the looming Brexit deadline and uncertainties.

In front of the famous front door, Johnson gave his first speech to the nation as he vowed to bring Britain out of the European Union by Oct. 31, saying "no ifs, no buts".

He said the critics, the doubters and the gloomsters are wrong, adding: "The people who bet against Britain will lose their shirts."

Johnson said although Britain will leave the EU by the end of October, and he was confident this can be done, adding: "We will crack this in 99 days, but we won't wait till then."

He said he was confident a deal can be done to resolve the Irish border question, without the need for what he described as an undemocratic backstop.

He said: "Never mind the backstop, the buck stops here."

But Johnson added Britain will prepare for Brussels refusing to do a deal with Britain.

He added: "To those who say it can't be done, do not underestimate this country."

Johnson's vehicle was briefly blocked by a human chain of protestors on its way to the Buckingham Palace.

The Opposition Labor Party leader Jeremy Corbyn called for a general election, saying that the new prime minister has "no mandate" of the British people.

Before Johnson became the prime minister, Philip Hammond had quit as Chancellor of the Exchequer, the most high profile in a slew of resignations.