South Korea has showcased cruise missiles and torpedoes at its biggest military parade in a decade sending a strong signal to North Korea over its "very grave" nuclear threats.

The military exhibited its might in front of US Defence Secretary Chuck Hagel and General Martin Dempsey, who are in the country for security talks.

The hour-long parade marked the 65th anniversary of Seoul's armed forces. Around 11,000 South Korean troops and 120 aircraft took part in the event.

A home-made cruise missile codenamed Hyeonmu 3 was unveiled during the parade. The missile is said to have a range of 1,500 km capable of striking neighbour North Korea.

Describing the situation in North Korea as "very grave", South Korean President Park Geun-hye said in her address: "While maintaining strong [South] Korea-US joint defence system, the government will secure anti-weapons of mass destruction capabilities, such as kill chain and the Korea Air and Missile Defence [KAMD] system, at an early date to make North Korea realise on its own that its nuclear weapons and missiles ... are useless."

She asserted that only a strong national defence will act as a deterrent to North Korea and bring it to the path of change.

"I hope you will do your duties with a mindset that the country's fate and unification of the Korean Peninsula hinge on the shoulder of every member of the Armed Forces."

Hagel reiterated US military support to South Korea in order to strengthen bilateral ties.