China called for "calm and restraint" on Wednesday after North Korea fired a volley of artillery shells and short-range missiles into the sea in an apparent show of force against ongoing joint military drills between South Korea and the U.S. North Korea fired seven artillery shells from multiple launchers into the East Sea on Tuesday with South Korea's defense ministry saying a Chinese civilian airplane with 202 passengers on board flew through the flight trajectory of some shells about 10 minutes after they were fired. Asked about the South Korean ministry's claim regarding the Chinese airline, China's foreign ministry spokesman Qin Gang told reporters during a regular press briefing, "We have noted relevant reports."    "We urge all relevant parties to exercise restraint, keep calm and be discreet in words and deeds so as to avoid a progressive escalation of tension," Qin said, adding that the situation on the Korean Peninsula is still facing "some uncertainties."    North Korea fired two short-range missiles on Monday into the East Sea after launching similar missiles last week. South Korea's defense ministry spokesman Kim Min-seok told reporters earlier in the day that the North's firing of artillery shells posed a "grave threat" to a civilian airline and was a violation of international aviation order.