Tens of thousands of people have taken part in celebrations to mark 30 years since the end of the Vietnam War.
Soldiers parade through the streets of Ho Chi Minh City
Military bands and marching peasant soldiers re-enacted the North Vietnamese victory in Ho Chi Minh City, formerly known as Saigon.
In Hanoi, costumed dancers on a stage mimicked the downing of US war planes and wept over their fallen comrades.
Prime Minister Phan Van Khai said the victory of 30 April 1975 was "forever written in our nation's history".
But he added that Vietnam still faced many challenges and should move on from the past and look to the future.
The tone of the celebrations was sombre but triumphant, reports the BBC's Kylie Morris in Ho Chi Minh City.
Liberation Day, as it is known in Vietnam, marks the victory of communist North Vietnamese forces over the US-backed regime in the south.
The government said it hoped the anniversary commemorations would help to revive patriotism and national pride among the young.
About two-thirds of Vietnam's 84 million population is under 30.
In Hanoi on Friday, Mr Khai told Vietnamese leaders, war veterans and foreign diplomats, including US Ambassador Michael W Marine: "Our people's victory in the resistance against the Americans for national salvation is forever written in our nation's history as one of the most glorious pages."
But he also said Vietnam needed to "avoid self-satisfaction, and realise the weaknesses and challenges posed to us".
And he added that his government advocated "friendly co-operation to strengthen relations with countries that took part in the Vietnam War."
Saturday's events included a parade by Vietcong veterans and a ceremony for those who were born 30 years ago to the day when communist tanks rolled through the gates of the city's Presidential Palace.
30 years ago the palace was the location for the formal surrender
Crew members of Tank 390, which at 1100 on 30 April knocked down the gates of the palace where the US-backed administration had spent its final hours, watched a re-enactment of the dramatic breakthrough which signalled the end of the war.
The Southern Vietnamese formally surrendered, marking the official end to a war which had claimed an estimated three million Vietnamese and some 58,000 American lives.
The red and yellow flag of Vietnam now adorns many of the streets and buildings of Ho Chi Minh City.
In front of the Presidential Palace, a large portrait of late President Ho Chi Minh, founder of today's Vietnam, takes pride of place.
The only high profile foreign visitor attending the celebrations was Cuban Defence Minister Raul Castro, President Fidel Castro's younger brother and apparent heir.
Cuba, along with the Soviet Union and China, were communist North Vietnam's key allies during the conflict.
More than 7,500 prisoners, including some political detainees, have been released this year as part of an anniversary amnesty.