Efforts to rescue those on board the burning Iranian oil tanker in the East China Sea were hindered by an explosion on the vessel. Reuters reported on Wednesday. The tanker, run by Iran’s leading oil shipping firm, caught fire after it collided with a Chinese freight ship carrying grain on January 7.

Rescue boats from China, South Korea and those deployed by the Iranian Navy are attempting to search for 31 missing sailors who were on board the tanker, Sanchi. The National Iranian Tanker Co-run vessel was carrying condensate, a highly flammable ultra-light crude, scheduled for delivery to South Korea.

Strong winds are also delaying the rescue mission. The wind speeds are expected to reduce by Thursday, China’s Transport Ministry said.

Iranian officials, however, seemed hopeful about the rescue mission. “If the crew have been able to reach some place like the engine room, then the chances of their rescue are high,” Iranian official Hassan Qashqavi told state news agency ISNA.

The tanker could burn for up to a month and the fuel released may pollute the ocean waters, South Korea’s Ministry of Oceans and Fisheries said on Wednesday.