* Port strike spreads across world No. 1 copper producer * Government calls for swift resolution * Half of trapped copper belongs to Codelco- minister SANTIAGO, April 4 (Reuters) - Around 9,000 tonnes of copper are unable to leave Chilean ports every day due to a spreading, costly port strike in the world's leading red metal producer, Mining Minister Hernan de Solminihac told reporters on Thursday. Were the situation to worsen, some smelters could have to halt their activities, he added. The Angamos port in the city of Mejillones, in Chile's mineral-rich north, launched a strike about three weeks ago to seek a 30-minute lunch break, and other ports have since joined the stoppage in solidarity, slamming the country's metal, fruit and wood exports. Chile's government on Thursday called for a swift solution to the stoppage, but there are no clear signs of when that could happen. The largely unexpected stoppage has turned into a major headache for many Chile-based miners, who produce a third of the world's red metal. Trading sources told Reuters they aren't aware of any strike-hit, Chile-based miners buying metal on the spot market to meet contract obligations. The stoppage helped push copper premiums in Singapore to their highest since May, Reuters reported on Thursday. It has also hindered the entry of certain mining supplies, according to the mining minister. Around half of all trapped copper belongs to state miner Codelco, he added. World No.1 copper miner Codelco has said nearly 60,000 tonnes of its copper is blocked, equivalent to around $500 million in revenue. Codelco is also facing a potential 24-hour work stoppage at all its divisions this month. Experts say presidential elections in November have also contributed to an uptick in labor unrest in Chile. Enthusiasm surrounding a stronger productive year in the Andean country on the back of new deposits and revamped old ones has somewhat been tempered by the port strike. Chile boosted its output of the red metal by 3 percent to 5.455 million tonnes during all of 2012.