South Korea's Defense Ministry says North Korea launched five missiles off its eastern coast Saturday, following similar tests earlier this week.
The Yonhap news agency quotes military officials as saying the missiles appear to be a type of short-range Scud missile.
The missiles were fired over several hours from Saturday morning, with the fifth missile launched in the afternoon.
South Korea's Joint Chiefs of Staff released a statement saying the military is fully ready to counter any North Korean threats and provocations.
Japan's Foreign Ministry has condemned the latest missile launches as a serious act of provocation against the security of neighboring countries.
The United States and North Korea's neighbors have described four North Korean missile tests Thursday as provocative, and called on the communist country to return to negotiations on de-nuclearization.
The the latest missile tests are taking place as the United States begins to celebrate is July 4 Independence Day holiday.
The missile tests add to the tensions on the Korean peninsula over North Korea's May 25 nuclear test and an April ballistic missile launch.
Britain's ambassador to Pyongyang Peter Hughes said Friday there was no evidence that North Korea was preparing to launch a long-range missile.
Japan defense officials last month said Pyongyang was preparing to launch a long-range missile capable of reaching the U.S. state of Hawaii around the U.S. Independence Day holiday.
However, South Korean news reports Friday quoted unnamed officials as saying the North was likely to launch a medium-range missile around the U.S. holiday, but not a long-range missile.
Separately, a South Korean news report Saturday said the North Korean cargo ship that changed course after being tracked by U.S. vessels appears to be carrying conventional small weapons, including Soviet-era rifles and missile launchers.
The report by Yonhap news agency quoted an official who asked not to be named because the information had to do with intelligence. The Kang Nam 1 was believed to be on its way to Burma.
The United Nations Security Council imposed a harsh new set of financial sanctions against North Korea last month in response to the nuclear and missile tests. The sanctions allow members to request a search of suspicious cargo to prevent Pyongyang from obtaining material needed for its nuclear and weapons programs.
Some information for this report was provided by AFP, AP and Reuters.