Aluminium stocks held at three major Japanese ports climbed for a 12th month to hit a record high at the end of March due to high level of imports and slow housing sector demand. The increase came as a surpise as Japanese buyers have reduced purchase volumes of January-March deliveries and some firms made efforts to cut inventories ahead of the end of the 2014 fiscal year. For many Japanese companies, the business year ends on March 31. “We were surprised to see another month of increase as traders and users were trying to reduce stocks by the end of March,” said a trader. Aluminium stocks held at Yokohama, Nagoya and Osaka grew 0.8 percent in March from a month earlier to 457,000 tonnes, Marubeni Corp said on Monday. The trading house collects data from those key ports. That broke the previous record set in February, the highest level in data going back nearly 15 years. An increased supply of semi-finished aluminium products in Asia due to Chinese exports has boosted the flow of aluminium ingots to Japan to look for buyers. Chinese exports of aluminium products grew about 19 percent last year. Meanwhile, Japanese imports of aluminium ingots for 2014 soared 16 percent from a year earlier to 1.698 million tonnes, the highest since 2010 and imports of aluminium alloys rose 11 percent to 1.125 million tonnes, the highest since 2008. But China’s export of unwrought aluminium and aluminium products, including primary, alloy and semi-finished aluminium products, fell 14.3 percent in March from the previous month, the latest trade data showed on Monday. “We assume behind the decline were falling premiums and LME prices, but it’s still unclear whether this will be a trend or just a temporary drop,” another Tokyo-based trader said. As regional supply climbed, the premiums that Japanese aluminium buyers pay over the London Metal Exchange (LME) cash price for primary metal shipments dropped in the April-June quarter for the first time in six quarters. Faced with high stocks and a supply surplus, aluminium prices have lost about 17 percent since their high in August 2014. Producers and traders say Japan’s overall demand for aluminium has been fairly stable, helped by solid demand in rolled products, but the extrusion segment has been hit by faltering housing starts.