HANOI, Vietnam (AP) — Vietnam's prime minister still retains a slim chance of challenging his rival, the ruling communist party chief, for the top job, according to a new interpretation of complicated rules disclosed at the start of a party congress that will name national leaders next week.

The Communist Party of Vietnam began an eight-day congress Thursday, which is held every five years for a usually orchestrated transfer of power to a new set of leaders.

But this time, a rare tussle emerged between party General Secretary Nguyen Phu Trong (pronounced New-yen Foo Chong) and his long-time rival, Prime Minister Nguyen Tan Dung (pronounced New-yen Taan Dzoong), that will be played out at the congress being attended by 1,510 delegates representing Vietnam's 63 provinces, ministries and party organizations.

Regardless of who becomes the chief, analysts say there will be little change in the way Vietnam is run, or in the economic policies that favor some free market reforms. However, Dung, who has spearheaded the reforms over the last five years, is backed by the business community and investors. He is also seen as being tougher on China, which has irked Vietnam by expanding its territorial ambitions in the South China Sea.

His rivals in Trong's camp have, however, accused him of economic mismanagement and corruption.

"Corruption and wastefulness remain serious problems ... causing discontent in the public, affecting people's trust in the party and the state," Trong warned in his speech to open the congress.

Dung, who has built up considerable support within the party through patronage, has ambitions to be general secretary, the de facto No. 1 in the collective leadership that rules Vietnam. The leadership comprises a 16-member Politburo, which looks after the day to day affairs, and a larger Central Committee that handles policy.

Earlier this week it was thought that Trong had sidelined Dung when a preparatory meeting agreed to continue with a controversial 2014 rule barring all but officially nominated candidates from consideration, with no new nominations allowed from the congress floor. Trong was endorsed as the general secretary candidate earlier this month.

However, on Thursday, Minister of Information and Communications Nguyen Bac Son gave a new interpretation of the rule that suggested Dung's case might not be hopeless.

Son said that while the Central Committee members' hands were tied, other delegates at the congress were free to nominate anyone they wished.

A Central Committee member such as Dung would be obliged by the rule to refuse nomination, but delegates could reject his refusal, said Son. Such a scenario could set up a showdown with Trong.

None of this drama, however, will be played out in the public. All proceedings of the Communist Party, which is empowered by the constitution to rule the country, are held behind closed doors. Even if there is an outright confrontation between the two leaders, the delegates are unlikely to take a vote, and the contest will be settled through negotiations and consensus.

Over the next week, the congress will review and set national and party policies, and select a new 180-member Central Committee. On one of the last days of the congress, the new Central Committee will meet to select a Politburo from among its ranks and pick one of them as party general secretary.

A united face will be presented on Jan. 28 when the congress will announce the names of the new general secretary, the prime minister, the president and the chairman of the National Assembly, along with other top posts. The actual selection of the last three leaders will be done by the National Assembly, which will be elected in May by popular vote, although the candidates will first have to be approved by the Communist Party.

A compromise is already believed to have been reached, under which Trong would stay as general secretary for two years instead of five, and a Dung supporter would become the chairman of the National Assembly. The prime minister's post would go to a neutral person and the president would be a Trong loyalist.

This configuration "would be a demonstrable loss for Dung" but it should not be "confused with an outright win by Trong," said Christian Lewis, a Vietnam expert at the New York-based Eurasia Group think tank. "It is instead a composition that reflects a desire for a balance and more consensus-driven decision-making at the very top," he wrote in a commentary.

The economic reforms Dung had been backing have brought a flood of foreign investment, created a fledgling stock market and helped triple per capita GDP to $2,100 over the past 10 years. At the same time, he is not without blemish. His rivals accuse him of economic mismanagement and failing to control massive public debt and non-performing loans of state-owned banks.

Vietnam is one of the last remaining communist nations in the world, with a party membership of 4.5 million, but like its ideological ally China, the government believes in a quasi-free market economy alongside a strictly controlled society that places several restrictions on its 93 million people.

Lewis said the new set of leaders will also support the current economic reforms and trade policy. Notably they remain committed to the Trans-Pacific Partnership with the United States and other key trade deals including the free trade agreement with the European Union.

Vietnam has an ambivalent relationship with China. Despite being its largest trading partner, China is also a security challenge. Beijing has been expanding its territorial assertions in the South China Sea, but Vietnam has pushed back against those claims. Dung has been seen as standing up to Beijing, not afraid to criticize it, while Trong was seen as being soft on China.

Associated Press writers Tran Van Minh in Hanoi, and Vijay Joshi and Grant Peck in Bangkok contributed to this report.