A wind-fed mountain fire that broke out in North Korea was spreading rapidly into the South Korean sector of the inter-Korean border Saturday, military authorities said.

The blaze, first spotted in the northern side of the 4-kilometer-wide Demilitarized Zone (DMZ) at around at 4:40 a.m., quickly spread past the border and reached within 600 meters of the nearest South Korean guard posts in the area, they said.

The South Korean military, helped by civilian firefighters, was trying to contain the blaze in the eastern sector of the border, military officials said, adding that no one was hurt.

No one was reported hurt, they said.

The size of burnt areas is estimated to have reached a radius of some 13 kilometers, but the exact damage has not been confirmed, they said.

South Korean fire fighters extinguished some embers that crossed the 2-meter-high barbed-wired fence erected on the South Korean side of the border, they added.

As part of measures to prevent the blazes from spreading to civilian areas, military authorities had three helicopters and additional workforces on standby, the officials said.

They have also blocked civilian movements in the nearby area and evacuated tourists from the Unification Observatory and the DMZ Museum.

The Korean DMZ, the world's most heavily armed, runs the width of the Korean Peninsula roughly along the 38th parallel. It is guarded by more than 2 million troops on both sides.

Bush and mountain fires often break out along the border, and one side accuse the other of intentionally starting them as part of military tactics.

Tension along the Korean border has spiked significantly in recent weeks as the two Koreas put their troops on full alert. North Korea has repeated threatened to start war in anger over new U.N. sanctions for its latest nuclear test in February and South Korea-U.S. joint military exercises.