A pipeline pumping oil from Myanmar to China started a trial operation on Wednesday, Chinese state media reported, Beijing's latest step to diversify energy imports into the world's second-largest economy.

The 771 kilometre (478 mile) pipeline will connect the world's top crude buyer with a deep-water port in western Myanmar, reducing China's dependence on oil transported through the Straits of Malacca.

Myanmar Vice President U Nyan Tun and Liao Yongyuan, general manager of Chinese energy giant CNPC, attended the opening ceremony, China's Xinhua news agency reported from Yangon.

CNPC and Myanmar's state-run Oil and Gas Enterprise (MOGE), completed the pipeline in late May last year after launching the project in June 2010, Xinhua said.

CNPC owns 50.9 percent of the project and MOGE the rest, according to the report.

Beijing was a key backer of Myanmar's military junta while it was under Western sanctions, but Thein Sein has increased ties with other countries since launching political reforms in 2011.

Myanmar is still a key part of China's bid to diversify its energy imports, however, and reduce its reliance on oil transported through the piracy hub of the Straits of Malacca.

Another pipeline pumping natural gas more than 2,500 kilometres from western Myanmar to southwest China went fully operational in 2013.

China also signed agreements worth $7.8 billion with Myanmar, state media reported in November, including deals to build power plants fuelled by natural gas.

The new oil pipeline will be able to transmit 22 million tonnes of crude a year from Myanmar's Made Island Port, which is due to be officially opened on Friday, Xinhua said.