Tanks rumbled through downtown Seoul on Tuesday, as South Korea staged its largest military display in a decade and paraded a missile capable of high-precision strikes anywhere in North Korea.

President Park Geun-Hye warned of the "very grave" threat posed by Pyongyang's nuclear weapons programme as the two-part display began at an airbase south of the capital in the morning.

Some 11,000 troops and 120 aircraft took part in the event, which showcased the military's most advanced weaponry as US Defence Secretary Chuck Hagel looked on.

Hagel was on a visit to underscore US commitment to its military alliance with South Korea where 28,500 US troops are currently stationed.

"The situation on the Korean peninsula... is very grave," Park warned in her speech at the event marking the 65th anniversary of the founding of South Korea's armed forces.

"North Korea adamantly continues to develop and upgrade its nuclear weapons," Park said, adding that the South had no option but to boost its military deterrent in response.

She specifically cited the development of sophisticated missile interceptor systems capable of neutralising a North Korean strike.

"I believe that the true purpose of the military lies not in fighting a war but preventing one," she said.

The defence ministry said Tuesday's display was the largest since 2003.

Hardware included the Hyeonmu 3, an indigenously developed cruise missile that was first deployed on naval destroyers in November last year and had not been shown in public before.

Two days after North Korea carried out its third nuclear test on February 12, the South's defence ministry called in the media for a video presentation showing the capabilities of the Hyeonmu, which has a range of 1,000 kilometres (around 600 miles).

"It is a precision-guided weapon that can identify and strike the office window of the North's command headquarters," ministry spokesman Kim Min-Seok told reporters at the time.

The missile was displayed again in the afternoon as a pared-down version of the parade moved to central Seoul, huge sections of which had been closed off to traffic for hours in advance.

The tanks, mounted heavy artillery, mobile missile launchers and marching soldiers paraded down a 1.4-kilometer route from the city's ancient South Gate towards the landmark Gyeongbok Palace.

Such events are generally considered more of a North Korean speciality, with massive, highly choreographed parades involving tens of thousands of goose-stepping troops regularly staged in Pyongyang.

The North's nuclear test triggered two months of heightened military tensions on the Korean peninsula, with Pyongyang threatening pre-emptive nuclear strikes on South Korea and the United States.

Those tensions have eased since, but acute concerns remain over the North's nuclear programme with signs that it is expanding its production of weapons-grade fissile material.

South Korea has cited the growing nuclear threat from Pyongyang to back its request for extending US command of combined US and South Korean forces in the event of war with the North.

South Korea is scheduled to take over wartime operational command in 2015, but defence policymakers now say they need more time to prepare for the transition.

Defense Secretary Hagel will discuss the issue with his South Korean counterpart Kim Kwan-Jin on Wednesday.

Meanwhile, the aircraft carrier USS George Washington is due to arrive in the South Korean port of Busan on Thursday, together with a guided-missile cruiser and destroyer, the US Navy said in a statement.

The George Washington is expected to take part in a joint naval exercise with South Korean vessels next week in the Sea of Japan (East Sea).