Boris Johnson has described David Cameron as a "brave and principled" man and expressed sorrow at his decision to resign after the UK voted to leave the EU.
The leading Brexit campaigner and frontrunner to succeed Cameron as Tory leader, sought to reassure young voters who have been made "anxious" at the referendum result.
Earlier this morning Cameron dramatically announced he will resign as prime minister following the UK’s decision to vote for Brexit.
Speaking outsideDowning Street, Cameron said he would step down in three months’ time. “I love this country and I feel honoured to have served it,” he said.
In a result that has sent shockwaves around the world, Leave won 51.9% of the total vote to Remain’s 48.1% after the final count. Turnout in the referendum was 71.8% - with more than 30 million people voting.
Jeremy Corbyn is to face a leadership challenge as early as this weekend after furious Labour MPs blamed him for Brexit, The Huffington Post UK has been told.
The Labour leader is held responsible by many of his own party in Parliament for the huge vote in working class areas that took the UK out of the EU.
Speaking at the Vote Leave headquarters in Westminster, Johnson said Brexit meant young people, who mostly backed a Remain vote, could "look forward to a more secure and more prosperous future".
"Young people who may feel that this decision in some way involves pulling up a drawbridge or any kind of isolationism, I think the very opposite is true," he said.
Johnson said the UK would be a "powerful, liberal, humane and extraordinary force for good in the world".
And he sought to reassure voters that "nothing will change over the short term" as the UK moves to wards exit from the EU.
Justice secretary and Brexit campaigner Micael Gove, a close friend of Cameron's, said the prime minister had "led this country with courage, dignity and grace".
Gove added: "He deserves to be remembered as a great prime minister."
Cameron said the result of the referendum meant the country needed “fresh leadership”.
“I fought this campaign in the only way I know how which is to say, directly and passionately, what I think and feel, head, heart and soul. I held nothing back, I was clear about my belief that Britain is stronger, safer and better off inside the EU,” he said.
Cameron added he expected the Conservative Party and government to have a new leader by the start of October. “I do not think it would be right for me to try to be the captain that steers the country to its next destination,” he added.