The city of Seoul erroneously issued an alert on Wednesday instructing residents to prepare for a possible evacuation after South Korea's military said North Korea fired what it claims to be a space launch vehicle southward.

The city sent the alert at 6:41 a.m., advising citizens to prepare to evacuate to underground shelters in relation to the North's launch of a projectile.

However, the interior ministry sent a mobile phone text at 7:03 a.m. informing recipients that the earlier warning was a false alarm.

Increased web traffic resulting from the alert briefly took down the nation's largest web portal, Naver.

Seoul Mayor Oh Se-hoon apologized for causing confusion, but said he doesn't think sending the emergency alert was a mistake. 

The interior ministry issued an alert for the western border islands of Baengnyeong and Daecheong at 6:29 a.m., which was lifted about an hour and a half later. 

The type of advisory issued on Wednesday calls for residents to prepare for a possible evacuation so that they can immediately move to safety if an air-raid warning is issued.

Earlier in the morning, the Joint Chiefs of Staff said that North Korea fired what it claims to be a "space launch vehicle" southward.