President Xi Jinping on Wednesday expressed profound mourning for former leader Jiang Zemin, hailing him as an outstanding leader of the great cause of socialism with Chinese characteristics.

Xi was speaking ahead of talks with President Thongloun Sisoulith of Laos, hours after it was announced that Jiang had died of leukaemia and multiple organ failure in Shanghai. He was 96.

"We profoundly mourn Comrade Jiang and will turn grief into strength to work in a concerted effort to build a modern socialist country in all aspects and advance the great rejuvenation of the Chinese nation in an all-round way in accordance with the plan of the 20th CPC National Congress," Xi said, according to the Xinhua news agency.

Xinhua reported that Xi described Jiang as an outstanding leader who enjoyed high prestige acknowledged by the party, the military and Chinese people of all ethnic groups.

The president said Jiang had been a great Marxist, a great proletarian revolutionary, statesman, military strategist and diplomat and a long-tested communist fighter. He was the core of the CPC's third generation of central collective leadership and the principal founder of the Theory of Three Represents, Xi added.

For his part, Thongloun expressed deep condolences and described Jiang as a close friend of Laos.