Vietnam is set to hold its biggest celebration of the fall of Saigon on its 50th anniversary on Wednesday, including Chinese troops for the first time after President Xi Jinping visited the country.

Thousands of excited citizens - many wearing T-shirts emblazoned with the Vietnamese flag - began gathering on the streets of the renamed Ho Chi Minh City on Tuesday, preparing to sleep out overnight ahead of the start of the display.

The celebrations come half a century after tanks of communist North Vietnam crashed through the gates of the city's presidential palace, defeating the US-backed South and delivering a painful blow to American moral and military prestige.

"I am proud of having contributed to liberating the south," said 75-year-old veteran Tran Van Truong who had travelled - dressed in full military uniform - from the capital Hanoi to see the parade.

Around 13,000 people, including veterans, soldiers and ordinary members of the public, will march down Ho Chi Minh City's Le Duan Street, a major thoroughfare which leads to the Independence Palace.

For the first time, more than 300 soldiers from China, Laos and Cambodia will take part in the spectacle. (Agencies)