By Ju-min Park

SEOUL Wailing air raid sirens and cell phone alerts calling for rare evacuations rattled residents of the South Korean capital, Seoul, early on Wednesday after North Korea launched what it said was a satellite.

North Korea launched the rocket toward the south, South Korea's military said, prompting emergency alerts and evacuation warnings in parts of South Korea and Japan.

"I was so panicked. 911 lines were busy and the internet was slow," said Lee Juyeon, 33, a resident in the densely populated city of 9 million who has a nine month old child. "So without knowing what was really happening, I was about to head down to a basement wearing a wrap carrier with my baby."

The sirens started in Seoul at 6:32 a.m. (2132 GMT Tuesday) as the city issued a "Presidential Alert" asking citizens to prepare for potential evacuation.

Then came a second mobile alert minutes later calling for an actual evacuation, which remained in place for at least 10 minutes until city said it was a false alarm sent in error.

Lee did not evacuate after seeing a television headline saying it was a North Korean space vehicle flying farther south, but she showed photographs of friends packing bags, readying to leave.

While residents of Seoul are used to living in the shadow of threats from their nuclear-armed neighbour, an element of complacency has crept in among many in the city about the risks and how to respond.

The two countries are still technically at war seven decades after the Korean War ended in an armistice.

'Alerts' and 'evacuation' were the most trending topics on Twitter in South Korea on Wednesday morning, with confused tweets scrambling to grasp what was going on or to find evacuation areas.

"Hey guys, given Twitter is still working, I guess it is not a war," one user using the handle @Kimisnim__ said.

(Reporting by Ju-min Park; Editing by Ed Davies and Lincoln Feast)