North and South Korea on Wednesday exchanged fire in waters off their disputed western sea border, officials and news reports in Seoul said, dpa reported.
North Korea fired several artillery shells into its part of the Northern Limit Line (NLL) around 9:05 am (0005 GMT), the South's Yonhap News Agency quoted a member of the Joint Chief of Staffs in Seoul as saying.
"We have confirmed North Korea's firing of several artillery shells, but they did not cross the NLL," Park Sung Woo said. "We are on high military alert."
The incident comes at a time of a renewed rise in tensions between the two Koreas after the North this month threatened a "holy war" against its southern neighbour.
There were no casualties or injuries in Wednesday's shooting, another South Korean official said.
South Korea responded by firing shoreline cannons into the air, an unidentified official from the president's office told Yonhap, but that report was not confirmed by the Defence Ministry or the Joint Chiefs of Staff.
North Korea on Monday declared parts of the disputed area in the Yellow Sea "no-sail" zones, raising speculation that Pyongyang was preparing missile tests.
In November, the two Koreas engaged in their first naval clash in seven years. South Korea's navy damaged a North Korean vessel that had violated the sea border.
North Korea does not recognize the Northern Limit Line, which was unilaterally drawn in 1953 by US-led United Nations forces after the Korean War.