Chinese President Hu Jintao will seek to cement friendly ties with Russia during his state visit starting Wednesday, observers say, but the relationship is still marked by lingering rivalries.

During the rule of Mao Zedong, China was under the thumb of the Soviet Union, but today the roles have been reversed -- a rising China is now the world's third largest economy, far ahead of Russia in eighth place.

Moscow still maintains superiority in some areas including nuclear deterrence, military armament and outer space.

The two countries nevertheless continue to work together on a host of issues, from negotiations on the nuclear programmes of Iran and North Korea to the Middle East, Sudan, non-proliferation and UN reform.

Their generally converging world view -- both call for a multipolar world that rejects US dominance on the international stage -- will be on display Tuesday at the first summit of BRIC nations with Brazil and India.

"You could say that Sino-Russian relations are in one of the better periods of their history," said Zhang Yao, an analyst at the Shanghai Research Institute of International Relations.

Since establishing a "strategic partnership" in 1996 -- the first for China -- and signing a friendship treaty in 2001, "relations have expanded in nearly every area," Zhang said.

Beijing and Moscow, which normalised ties in 1989, signed an agreement in 2004 putting an end to complex disputes along their 4,250-kilometre (2,635-mile) border.

"There has been a big investment here. They wanted to settle all the accounts of the past," said a Western official who is an expert on Sino-Russian ties.

While the West has maintained an arms embargo on Beijing, Russia has been China's main military supplier, even if sales have fallen off in the last five years.

Commercial relations have also evolved between the two sides, although not at the same pace as diplomatic ties, with bilateral trade hitting about 50 billion dollars in 2008.

On energy, Beijing and Moscow have sealed an agreement for the delivery of Russian crude oil to China via the Siberian-Pacific pipeline.

"It's a very complex agreement, involving very large sums, showing that on the energy issue they are capable of creating a long-term relationship," said the Western official.

Despite all the areas of cooperation, rivalries and suspicions remain.

Moscow now views Beijing with "a mixture of admiration, jealousy, unease and annoyance," said Jean-Pierre Cabestan, a China expert and co-author of a book on Sino-Russia ties.

Moscow is irritated by "such assurance, such tranquil force (that the Chinese possess) ... as well as the incapacity of the Russian economy to rise to the ranks of the five largest economies in the world," he said.

In Central Asia, a traditional stage on which their rivalry has been played out, the two nations are competing for access to the region's lucrative oil and gas reserves, said the expert.

Russia has been wary of China's strengthened economic and diplomatic ties with countries that were once part of Moscow's sphere of influence.

Moscow has also been concerned about what it perceives as the threat posed by Chinese immigration -- not just to Russia's Far East, but also to the European part of Russia.

Russia is particularly worried about energy-hungry China's interest in the region's raw materials, with Beijing seen in some Russian quarters as a plunderer of national energy resources.

On the other hand, the Chinese, like the Europeans, see Russia as a rather untrustworthy energy partner.

The relationship is further complicated by the fact that Beijing and Moscow both are focused on bolstering ties with the United States.

"The relationship with Washington has top priority, both at the political level and commercially," said Cabestan.