A replica tank rolled through the streets of the city
Vietnam has marked 35 years since the end of its war by staging a re-enactment of the fall of the Saigon.
Thousands of troops marched through the streets of what is now officially called Ho Chi Minh City to mark the day the communist North claimed victory.
Vietnam's President Nguyen Minh Triet used the event to praise the country's economic development.
The Vietnam War claimed the lives of three million Vietnamese and some 60,000 US soldiers.
Tens of thousands of people gathered in front of the former presidential residence, now called Independence Palace, in Ho Chi Minh City, to watch the military and cultural display.
The BBC's Nga Pham in the city said the events began in the early hours to avoid the heat of the day, with a play recounting the history of the country from ancient times to when the North's tanks smashed through the gates of the palace, leading to the surrender of the southern government.
A replica tank drove through the city to the palace, greeted by cheers from the crowds.
The event was an emotional one for many who lived through the war itself, with some people crying as they watched the display.
"We are here today, very emotional, and thinking of what happened 35 years ago," said Vu Dang Toan, a member of the tank unit involved in the victory in 1975.
"It was a great victory, it was very quick to liberate Saigon and the country is reunited."
Others said it was a time to remember those who died in the devastating conflict.
"I think of my comrades who sacrificed their lives for the country. We feel happy but we always are grateful to those who died for our country," said 80-year-old veteran Vu Thi Nham.
The ceremony in Ho Chi Minh City - named after the man seen as the founder of the revolution - was attended by leaders and dignitaries from Cuba, Russia, Laos and Cambodia.
The ceremony led to some mixed reactions
President Nguyen Minh Triet praised the country's development since the war, saying its "economy has steadily grown while socio-political stability and national defence have been guaranteed".
"The country's status in the international arena has been lifted while its people's lives increasingly improved," Vietnam News quoted him as saying.
Mr Triet attributed the country's success to the Communist party, armed forces and the Vietnamese people.
By the time the US-backed South Vietnamese government collapsed, millions of people had died. Many thousands on both sides are still missing in action.
The war also left deep divisions within the nation, with millions fleeing Vietnam in fear of persecution from the new regime, says our correspondent.
Vietnam remains under communist rule and the government keeps tight control over politics and the media.
But its economy has improved dramatically since the war, and diplomatic relations have resumed with the United States.
Our correspondent says the celebrations acted as a reminder of the atrocities of the war as well as a sign of how keen the Vietnamese people are to develop their country.