BEIJING - China's June aluminium imports surged by more than 490% from a year earlier, customs data showed on Thursday, to their highest in 11 years, as traders snapped up lower-priced overseas metals.

Imports of unwrought aluminium and aluminium products into China, the world's top aluminium producer which rarely imports large amounts of the metal, were 288,783 tonnes last month, the General Administration of Customs said.

That was more than double May's imports of 119,145 tonnes and a jump of 493.1% from June 2019, customs said, as buyers took advantage of the differences between domestic and international prices. Imports were the highest since June 2009.

China shipped out 354,038 tonnes of unwrought aluminium and aluminium products last month, down 30% year-on-year, customs data showed.

Imports in January to June were 816,592 tonnes, up 219.2% year-on-year, while exports were 2.37 million tonnes, down 20.6% from a year earlier, leaving China a net exporter of 1.5 million tonnes in the first six months of 2020.

Shanghai aluminium prices SAFcv1 rose 23% in the second quarter as Chinese consumption roared back from a coronavirus-driven collapse. However, London prices CMAL3 only gained 6.1% in April to June amid sluggish demand outside of China, and after a 15.7% dip in the first quarter.

The spread between Shanghai and London cash aluminium prices widened to almost 1,800 yuan ($258.16) a tonne in late May, the most since January 2014, opening up a so-called arbitrage for primary metal to head to China from overseas.

China's imports of unwrought, alloyed aluminium - described by analysts as secondary ingots - have also been rising in recent months to compensate for curbs on inbound scrap metal shipments.

Customs is due to release a breakdown of imports by origin and type of aluminium and other commodities on Saturday.

($1 = 6.9723 yuan)

(Reporting by Tom Daly and Min Zhang in Beijing, Mai Nguyen in Singapore; Editing by Christian Schmollinger) ((tom.daly@thomsonreuters.com; +86 10 5669 2119;))