SEOUL — A stricken Iranian oil tanker in the East China Sea could burn for as long as one month, South Korea's Ministry of Oceans and Fisheries told Reuters on Wednesday, as the blaze raged for a fourth day following a collision with a freight ship. Dozens of rescue boats battled strong winds, high waves and poisonous fumes to comb a 900 sq. nautical mile area for 31 missing sailors and tame the fire, amid growing concerns the listing ship may explode or sink. We believe flames would last for two weeks or a month considering previous cases of oil tank accidents, said official Park Sung-dong. What we are concerned about at this moment is the bunker fuel, which could contaminate water if (the ship) sinks, the ministry official said. The tanker Sanchi (IMO:9356608), run by Iran's top oil shipping operator, National Iranian Tanker Co, collided on Saturday with the CF Crystal (IMO:9497050), carrying grain from the United States, about 160 nautical miles off China's coast near Shanghai. The Sanchi was delivering 136,000 ton of condensate, a highly flammable ultra-light crude, to South Korea. The cargo of about 1 million barrels is worth some $60 million. The Chinese government said late on Tuesday it had not found a large-scale oil leak, and the condensate was burning off or evaporating so quickly that it would leave little residue — less than 1 percent — within five hours of a spill. That reduces the chances of a crude-