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.

South Korea's new cruise missiles Hyunmoo-3 and Hyunmoo-2 are displayed during events to mark the 65th anniversary of Armed Forces Day, in SeongnamReuters
South Korea's Israeli-made Spike missiles are seen during events to mark 65th anniversary of Armed Forces Day, in SeongnamReuters
Black Eagles South Korean Air Force aerobatic team perform manoeuvres during celebrations to mark 65th anniversary of Korea Armed Forces Day, in SeongnamReuters
South Korean Air Force F-15K fighter jets fly in sky during celebrations to mark 65th anniversary of Korea Armed Forces Day, in SeongnamReuters
Black Eagles South Korean airforce aerobatic team perform manoeuvres during celebrations to mark 65th anniversary of Korea Armed Forces Day in SeongnamReuters
Coloured contrails are seen behind South Korean Air Force F-16 fighter jets in sky during celebrations to mark 65th anniversary of Korea Armed Forces Day, in SeongnamReuters
Man takes photographs of heart-shaped contrail left in sky by Black Eagles South Korean Air Force aerobatic team during celebrations to mark 65th anniversary of Korea Armed Forces Day, in SeongnamReuters
Members of South Korea's Underwater Demolition Team march during the 65th anniversary of Korea Armed Forces Day, in SeongnamReuters
Members of Special Warfare Command give demonstration of their taekwondo skills during celebrations to mark 65th anniversary of Korea Armed Forces Day, in SeongnamReuters
South Korean President Park speaks with Defense Minister Kim during inspection of troops as part of celebrations to mark 65th anniversary of Korea Armed Forces Day in SeongnamReuters
South Korean President Park Geun-Hye waves as she inspects troops during a ceremony marking the 65th anniversary of the founding of South Korea's Armed Forces at an air base in SeongnamReuters