HO CHI MINH CITY/HANOI -- Vietnamese President Tran Dai Quang, once seen as a potential successor to the Southeast Asian nation's top leader, died on Friday at the age of 61, according to state media.
The report said he died at a hospital in Hanoi after suffering from a serious illness. Vice President Dang Thi Ngoc Thinh will serve as acting president until a new president is named by the Communist Party's Central Committee and elected by the National Assembly.
Quang, who held the country's second-highest office, had rarely been seen in public in recent months, arousing speculation about his health or a power struggle in the Vietnamese leadership. In August, Quang missed a number of key events, including one commemorating the anniversary of the founding of the People's Public Security Force.
Communist Party General Secretary Nguyen Phu Trong, the most powerful official in the country, recently stepped up diplomatic activities in the absence of the president, who plays a mostly ceremonial role.
Potential candidates to replace Quang include Tran Quoc Vuong, executive secretary of the party's secretariat, and deputy prime minister Vuong Dinh Hue. Both men are close to Trong. A decision will likely be made at the National Assembly in late October.
Trong could take over the position himself, as many in Vietnam argue that offices of general secretary and president should be held by the same person -- as is the case in China -- to avoid diplomatic confusion.
Either way, Quang's death accelerates the concentration of power in Trong's hands. That has implications for Hanoi's relationship with China, which is Vietnam's largest export market and shares deep political and historical ties with the country. Trong is regarded as a member of the Vietnamese leadership's China-leaning faction. Intractable issues remain, however, such as territorial disputes in the South China Sea.
Quang was one of the socialist nation's leadership quartet, along with Trong, National Assembly Chair Nguyen Thi Kim Ngan and Prime Minister Nguyen Xuan Phuc. He had been seen as a likely candidate to replace Trong, who is 73, a fact that is fueling talk of a handover of power as early as next year.
Politburo member Quang was elected president in 2016. He revealed little as to whether he was a reformer or a hard-liner during his tenure. He also served as chairman of the national defense and security council and head of the central steering committee for judicial reform.
Carlyle Thayer, a Vietnam expert and professor at the University of New South Wales, described Quang as a "gray man" who had risen to become a key party power broker through his control of the influential Ministry of Public Security.
Rampant corruption in the ministry was uncovered by a campaign against official misconduct launched by Trong's campaign. Speculation arose last summer that Quang had been stripped of power as a result, but he reappeared in November to host the Asia-Pacific Economic Cooperation forum in Danang.
"It's too early to make a definitive judgment about Quang's contribution -- or to guess who his successor might be -- not least because he was only halfway through his first term in office," Thayer said.
More power for Trong could also complicate relations with Japan, Vietnam's largest source of economic aid and foreign direct investment. As Cambodia, Laos and other nations in the region lean toward China, Tokyo seeks to maintain strong ties with Vietnam. But it is losing channels for influencing Hanoi.
In March, former Transportation Minister Dinh La Thang -- a prominent Japan supporter close to former Vietnamese Prime Minister Nguyen Tan Dung, who lost a power struggle in 2016 -- was handed a 30-year jail sentence for mismanagement at state-owned PetroVietnam.
Quang was born in Ninh Binh Province, about 100 km from Hanoi. He held a master's degree in Chinese and a doctorate in law.