SEOUL, Oct 1 (AFP) - North Korea fired two short-range ballistic missiles towards the sea off the east coast on Saturday, South Korea's military said, marking Pyongyang's fourth launch in a week as it ratchets up tension around the Korean peninsula.

The launch comes after the navies of South Korea, the United States and Japan staged trilateral anti-submarine exercises on Friday for the first time in five years, and follows U.S. Vice President Kamala Harris' visit to the region this week.

The two short-range missiles were launched from Sunan, north of the North Korean capital Pyongyang, South Korea's Joint Chiefs of Staff said in a statement. It estimated the range at 350 kilometres (217.5 miles) at 30 km altitude and speed of Mach 6.

Japan's coast guard also reported at least two suspected ballistic missile tests by Pyongyang. The missiles flew 400 km and 350 km, reaching an altitude of 50 km, Japan's State Minister of Defence Toshiro Ino said.