North Korea fired short-range rockets into the sea off its east coast on Wednesday morning, South Korea's Yonhap News Agency said, one day ahead of a state visit by Chinese President Xi Jinping to Seoul.
North Korea, which tested two short-range missiles on Sunday in violation of a UN ban, is expected to be high on the agenda when Xi meets his South Korean counterpart, Park Geun-hye.
Xi, who is due to arrive in Seoul on Thursday in his first visit to South Korea since taking office last year, is reciprocating Park's visit to China a year ago.
North Korea's nuclear and missile programme, and its plans to hold a fourth nuclear test, will dominate the agenda, officials in Seoul said.
A South Korean Ministry of Defence official was unable to confirm what kind of weapon was fired, but said they were assumed to be 300 mm rockets launched from one of the North's many Multiple Rocket Launchers.
U.N. resolutions prohibit North Korea from procuring and using ballistic missile technology, but short range rocket launchers are not included in the ban.