LONDON (Reuters) - London-listed miner Glencore ( GLCNF ) has declared force majeure on copper shipments from its Chilean Altonorte smelter, where production has been suspended, two industry sources said.

Companies declare force majeure when unexpected circumstances prevent them from meeting contractual obligations.

The sources did not know how long operations at Altonorte, which has capacity to produce 350,000 metric tons of copper a year in anode form, would be suspended.

Glencore ( GLCNF ) declined to comment.

Altonorte's output is a fraction of refined global copper supplies estimated at around 26 million tons, but a long suspension could widen the deficit some analysts are expecting this year.

Much of the copper produced in Chile is shipped to the U.S., where prices on COMEX have soared to record highs on worries about shortages due to tariffs on imports of the metal used in the power and construction industries.

The most active copper contract on COMEX for settlement in May hit $5.3740 a lb or $11,847 a ton on Wednesday.

The force majeure was first reported by Bloomberg on Tuesday.