The nation's aviation bureau mistakenly reported a North Korean missile launch as it sought damage reports from airports after the biggest earthquake in the western part of the country since 1995.

The bureau sent the prewritten email alert to 87 airport offices after the temblor hit at 5:33 a.m. Saturday, the Transportation Ministry said in a statement. The message was retracted at 5:39 a.m., and it may have caused a delay as long as four minutes to one flight, according to the statement.

The ministry will require that two officials check all weekend mobile-phone alerts prior to distribution to prevent any similar mistake, it said in an emailed release last night.

The 6.3-magnitude quake was the biggest in the region since the 7.2-magnitude Great Hanshin Earthquake in January 1995, Japan's Meteorological Agency said. There were 23 people injured due to the tremor, the Fire and Disaster management Agency said in a statement yesterday. No damage to nuclear plants was reported, it said.