A US military helicopter has crashed near the North Korean border, a South Korean defence official says, with no reported casualties.

The helicopter, identified by the Yonhap news agency as a UH-60 Black Hawk, came down in Cheolwon county, which touches on the border with North Korea, a defence ministry spokesman told AFP on Tuesday.

The precise cause of the crash was not immediately clear, but the incident occurred during ongoing South Korea-US joint military exercises.

Yonhap quoted emergency rescue workers as saying the 12 service personnel on board the helicopter had survived the crash, which comes at a time of heightened military tensions on the Korean peninsula.

North Korea has condemned the joint exercises as a rehearsal for invasion, and made a series of dire threats of military retaliation.