President Xi Jinping sent a message of condolence on Friday to Nguyen Phu Trong, general secretary of the Communist Party of Vietnam Central Committee, over the death of Vietnamese President Tran Dai Quang.

On behalf of the Communist Party of China and the government and people of China, as well as on his own behalf, Xi, also general secretary of the CPC Central Committee, expressed deepest condolences to Trong, the CPV and the Vietnamese government and people.

"We feel deeply grieved over Quang's death," Xi said.

Quang was an outstanding leader of the party and the country of Vietnam, and had made significant contribution to Vietnam's national development as well as its reform and opening-up, he said.

Xi said that Quang, as an intimate comrade and friend of the Chinese people, was committed to inheriting and carrying forward the traditional friendship between the two countries and actively promoting the development of the China-Vietnam comprehensive strategic cooperative partnership.

He said he believes that the CPV and the Vietnamese government and people will turn sorrow into strength under the strong leadership of Trong, and continuously achieve new progress in socialist construction.

Xi also asked Trong to convey his deepest sympathy to Quang's family.

Quang died on Friday morning in a hospital in Hanoi of a "serious illness despite efforts by domestic and international doctors and professors", Vietnam Television said. He was 61.

Quang was born on Oct 12, 1956, in Ninh Binh province. He held a doctoral degree in law and a master's degree in Chinese and was conferred the title of professor in 2009.

In April 2016, the National Assembly of Vietnam, the country's top legislature, elected Quang as president.

State-run online newspaper VnExpress quoted a former health minister and the head of a national committee in charge of leaders' health, Nguyen Quoc Trieu, as saying that Quang had contracted a rare and toxic virus in July last year and had traveled to Japan six times for treatment. He did not specify the virus.

Vietnam's Constitution provides for the vice-president to perform the president's duties should he be unable to work.

The National Assembly is scheduled to convene a session next month and is expected to elect a new president.

Xinhua, AP and Reuters contributed to this story.