(Recasts, updates with official prices)
LONDON, Aug 28 (Reuters) - Nickel prices hit their highest in a week on Wednesday as speculators bought on fears of shortages from major producer Indonesia, while at least half of London Metal Exchange inventories were under the control of one party.
Nickel, mainly used to make stainless steel, has shot up about 50% so far this year, fuelled by concerns that Indonesia will move forward a mineral export ban due in 2022.
"The price rise is exaggerated," said Commerzbank analyst Daniel Briesemann, adding that the price gains were not supported by supply and demand fundamentals.
"Lower exports of nickel ore should at least in part be balanced by higher exports of higher-value nickel products, so the impact would not be as severe as appears at first glance."
Benchmark nickel was the strongest performer on the LME, advancing 1.5% to $15,930 a tonne in official open-outcry trading after touching $16,000, the highest since Aug. 21.
The net speculative long position of nickel on the LME had expanded to 20% as of Friday's close, a fresh year-to-date high, Alastair Munro at broker Marex Spectron said in a note.
* NICKEL STOCKS/TIME SPREAD: One party holds 50% to 80% of available LME inventories, data showed, leading to tight supplies in the LME system, traders said.
They said this also likely contributed to a jump in the premium of cash LME nickel over the three-month contract <CMNI0-3> to $79 a tonne by Tuesday's close, the highest in a decade.
* NICKEL WASTE: Waste from a nickel plant in Papua New Guinea owned by Metallurgical Corporation of China spilled into the adjacent Basamuk Bay over the weekend, three sources told Reuters on Wednesday.
* CHINA RATES: Deteriorating Sino-U.S. trade ties and interest rate reforms are fuelling speculation China will start cutting key rates from next month, but bankers expect borrowing costs to come down only gradually.
* CHALCO: Chinese aluminium giant Chalco's, production of the metal fell more than 8% in the first-half of 2019 from the same period a year earlier, data showed, highlighting the impact of low prices on Chinese smelters.
* PRICES: LME copper shed 0.2% to trade at $5,673 a tonne in official rings, aluminium dipped 0.1% to $1,758.50, zinc lost 0.6% to $2,259.50, lead fell 0.7% to $2,085, while tin gained 0.6% to $15,850.
* For the top stories in metals and other news, click or ($1 = 7.0928 Chinese yuan) (Reporting by Eric Onstad; Editing by Ken Ferris and Edmund Blair)