SEOUL (Reuters) - South Korea s coast guard said it fired 249 warning shots over a  group of Chinese fishing boats  swarming around  one of its patrol ships in South Korean waters, prompting a call for restraint from Beijing.  South Korean coast guard vessels regularly chase Chinese boats suspected of fishing illegally in South Korean waters, at times sparking violent confrontations, complicating a relationship which is key to efforts to try to rein in North Korea s nuclear and missile programs. A fleet of 44 Chinese fishing boats fortified with iron bars and steel mesh on Tuesday began to rush the patrol boat which broadcast warnings to steer clear, the coast guard said.  The coast guard vessel fired 249 shots over the boats until they retreated.   The Chinese fishing boats sought to swarm around and collide with our patrol ship, ignoring the broadcast warnings,  the coast guard said in a statement.  China, which has in the past lodged diplomatic protests with South Korea over the use of force by its coast guard, expressed  serious concern  about the reports.   We hope that South Korea appropriately handles the relevant issue and in the course of law enforcement takes no extreme actions that endanger people s safety,  foreign ministry spokeswoman Hua Chunying told reporters in Beijing.  Seoul s foreign ministry said the coast guard followed domestic law in its use of weapons in a  legitimate step  against the boats which made a  mass violation of the country s waters for illegal fishing . In September last year, three Chinese fishermen were killed in a fire on their boat when a South Korean coast guard crew trying to apprehend them for illegal fishing threw flash grenades into a room where they were hiding, according to the South Korean coast guard.  A month later, two Chinese fishing boats illegally fishing in South Korean waters crashed into and sank a coast guard vessel, the coast guard officials said. 