The broadcasts, in rolling bursts from walls of loudspeakers at 11 locations along the heavily militarized border, blare rhetoric critical of the Pyongyang regime as well as "K-pop" music.
The unification ministry in Seoul said there has been no government decision on what North Korea needs to do to end the broadcasts, which began at noon local time (3am GMT/2pm AEDT) on Friday.
North and South Korea traded artillery fire in August after Pyongyang demanded a halt to the loudspeaker broadcasts.
The rapturous response in North Korea was in stark contrast to worldwide condemnation of the provocative move.
Pyongyang earlier said it had successfully tested a miniaturised nuclear hydrogen bomb on Wednesday. Park also spoke to Japanese Prime Minister Shinzo Abe on Thursday. The US and United Nations have also announced that they're working on sanctions against the North as a punitive measure.
A US government source said Washington believes North Korea had set off the latest in a series of tests of atomic bombs. B-2 and B-52 bombers are capable of delivering nuclear weapons.
Cho said the fourth nuclear test is a direct violation of promises and obligations to the global community and the United Nations Security Council, and a serious violation of the August 25 North-South agreement.
Many experts have said the blast wasn't large enough to be a hydrogen bomb.
"But we can possibly say that it is a boosted fission bomb at the most", Yang UK, a senior research fellow at the Korea Defence and security Forum said. An explosion two to five times more powerful would have been reported if it were successful, the official said, requesting anonymity because of department rules.
The South's presidential office made the announcement Thursday, in retaliation for the bomb tests.
"As a small country, we have suffered in the past, but now we have got a hydrogen bomb, there is nothing greater than this".
In turn, Cook said, Han emphasized the strength of the U.S.-South Korea alliance and its vital role in assuring peace and stability on the Korean Peninsula and across the Asia-Pacific.
US Republicans and Democrats in the House of Representatives could join forces in a rare display of unity to further tighten sanctions on North Korea. "This new nuclear test may inspire North Korea in the short-term".
US aircraft created to detect evidence of a nuclear test, such as radioactive particulate matter and blast-related noble gases, could be deployed from a USA base on the Japanese island of Okinawa.