Iron ore futures in Asia tumbled as rising port inventories in China, the biggest buyer, hurt prices that have been propelled higher this half by an improved economic outlook and heightened investor speculation. Futures on China’s Dalian Commodity Exchange fell as much as 5.7 percent to 435.5 yuan ($67.25) a metric ton and traded at 439 yuan at 11:04 a.m. local time, while Singapore’s SGX AsiaClear contract sank as much as 5.8 percent to $58.51 a ton. Losses in the contracts in Asia typically presage a drop in the Metal Bulletin Ltd. price for 62 percent content spot ore in Qingdao, which is updated daily. Iron ore’s gains in the opening months of 2016 wrong-footed many forecasters after China added stimulus, presiding over an unexpected rebound in the property sector and the surge in speculative trading. Port inventories rose 1.2 percent to 98.5 million tons last week, the highest in more than a year, according to data from Shanghai Steelhome Information Technology Co. Holdings last topped the 100 million ton mark in March 2015. “May marks the period where steel demand typically starts to slow after a busy season,” Xia Junyan, an analyst at Everbright Futures Co., wrote in a note on Tuesday. “Port stockpiles of iron ore have remained near 100 million tons, indicating that supply is relatively abundant.” Ore with 62 percent content delivered to Qingdao surged 5.3 percent to $66.24 a dry ton on Friday, according to Metal Bulletin Ltd. The commodity has soared 52 percent this year, topping $70 last month for the first time since January 2015. Last year, it bottomed at $38.30. A manufacturing gauge for China’s steel industry signaled the first expansion in two years, adding to signs that demand is rebounding in the top user. The steel purchasing manager’s index rose to 57.3 in April from 49.7 a month earlier, according to official data on Sunday. Readings above 50 indicate expansion.