MOSCOW (CNN) -- China's President Jiang Zemin arrived in Moscow on Sunday for an informal "no-neckties" meeting with Russian President Boris Yeltsin intended to underscore expanding cooperation between the two countries.

But the Chinese leader's scheduled talks became complicated by Yeltsin's sudden illness and hospitalization. Kremlin officials said Jiang was invited to meet with Yeltsin Monday at the Central Clinic Hospital, where the Russian leader is being treated for pneumonia. The talks had earlier been scheduled at the Ogaryovo residence near Moscow and were expected to concentrate on trade, border issues, and countering the perceived U.S. domination of the post-Cold War world order.

Russia's deep economic crisis has cast a shadow over the bilateral summit, with Chinese humanitarian aid to its huge northern neighbor likely to feature on the agenda, Interfax news agency reported on Sunday.

Such a possibility highlights the reversal of fortunes between Russia and China, which considers itself a developing country and was a Soviet disciple and aid recipient in the 1950s when Jiang himself studied in Moscow.

Yeltsin's performance during the summit will be under intense scrutiny. Many have questioned whether he can bear the weight of his official duties, given his ongoing health problems.

The 67-year-old Kremlin leader has spent much of the past month and a half recovering from what his doctors say is exhaustion and poor blood pressure. He has canceled several overseas trips and has made only brief public appearances, mainly to welcome visiting foreign leaders.

However, Russian officials are upbeat about ties with China.

"I want to stress that this is the first ever informal Russo- Chinese summit, which underlines the high level of trust in our bilateral relationship," Russian Foreign Ministry spokesman Vladimir Rakhmanin said.

Despite Russia's crisis and Asia's own financial woes, he said the long-term prospects for trade were bright. Russia and China have pledged to boost annual bilateral trade, which fell 10 percent last year to around $6 billion, to $20 billion by 2000.

Yeltsin has long championed the personal brand of summitry he calls "no-neckties" diplomacy and has often used his friendly rapport with Western leaders like former German chancellor Helmut Kohl to win their support for his policies.

Jiang, who speaks some Russian and once worked in a Moscow auto factory, also seemed to welcome such informal meetings.

"This form of contact makes it possible in an informal and calm atmosphere to discuss a broad range of problems, to find mutual understanding and behave more sincerely and in a relaxed manner," he told Russia's ITAR-Tass news agency last week.

Jiang was also scheduled on Monday to meet with Prime Minister Yevgeny Primakov and other senior government and parliamentary officials.

Primakov, now responsible for the day-to-day management of Russia, met Jiang last week when he stood in for Yeltsin at a gathering of the Asia-Pacific economic forum in Malaysia, where Moscow formally joined that grouping.

A former foreign minister, Primakov seeks to expand Russia's role in the Asian-Pacific region. Jiang's trip follows soon after an official visit to Moscow by Japanese Prime Minister Keizo Obuchi, the first of its kind for 25 years.

Kremlin spokesman Dmitry Yakushkin said Yeltsin and Jiang would issue a joint statement after their talks hailing the completion of demarcation work on the shared 4,300-km (2,800- mile) border between Russia, the world's largest country geographically, and China, the world's largest in population.

"For the first time in the history of relations between Russia and China we will have a demarcation of our common border throughout its entire length. ... For the first time a unique model of border safety will be created on the Asian continent," Yakushkin said on Friday.

Yeltsin and Jiang, at a Beijing summit last November, resolved a dispute over implementation of a 1991 accord mapping out the border.

Border disputes erupted into armed clashes in the 1960s when the two giants were vying for supremacy in the Communist world.

On Tuesday, Jiang travels to the Siberian city of Novosibirsk where he will visit a nuclear institute and address scientists. He flies on to Japan on Wednesday.

Jiang had planned to invite Yeltsin to visit China next year for a seventh summit meeting, ITAR-Tass said Sunday, and quoted Kremlin sources as saying the Kremlin is prepared to accept the invitation. Whether Yeltsin will be able to undertake the journey remains undetermined.

Reuters contributed to this report.