Copper prices hit a three-week high in London on Thursday amid speculation that demand is strengthening in part because of China, Bloomberg reported. Copper for delivery in three months rose 5.8% to US$4,794 a metric ton on the London Metals Exchange (LME), the biggest intraday jump since April 14. Meanwhile, copper for delivery in August closed at US$5,568 on the Shanghai Futures Exchange. According to LME research, copper booked for delivery now makes up 18% of total stockpiles, up from about 1% at the start of the year. Inventories at LME-monitored warehouses in Singapore have plunged 91% since peaking in April. The metal, used in electrical wiring and plumbing, has gained 54% in London so far this year, buoyed by demand from China. The country imported a record amount of copper in March. Nickel, tin and zinc prices are also rising.