Vietnam on Monday named a long time rival of Prime Minister Nguyen Tan Dung as its new president, a largely symbolic post in the communist nation.

Truong Tan Sang, 62, was confirmed for the job by a vote of the one-party National Assembly, after he was formally nominated as the sole candidate over the weekend.

"He has been voted president," with more than 97 percent of 496 votes, said an official from the Assembly's press centre, asking not to be named.

Sang, the country's ninth president, will take on a post first held by revered founding father Ho Chi Minh.

Sang had been the ruling Communist Party's de facto number two since 2006 and mounted an aggressive challenge for the prime minister's job before the party's secretive January congress, which determined top leadership posts.

Those positions are being confirmed this week, and Dung is expected to be elected to another term as prime minister in a National Assembly vote on Tuesday, cementing his place as the country's most powerful politician.

Despite their rivalry, the relationship between Dung and Sang is expected to be cordial as the prime minister focuses on trying to bring stability to a troubled economy, said an Asian diplomat.

"He's not about to pick a fight with his rival," said the diplomat, requesting anonymity.

Like Dung, Sang is a native of southern Vietnam. A student militant imprisoned by the then US-backed South Vietnam regime, Sang later became mayor of Ho Chi Minh City.

Sang replaces Nguyen Minh Triet, who served one term.