South Korea's president Monday defended the proposed deployment of a US anti-missile system as an act of self-defence against North Korea, as hundreds of residents shaved their heads in protest at the plan.

Tensions have been running high on the divided Korean peninsula since the North carried out its fourth nuclear test in January and followed up with a series of missile tests.

South Korea responded last month by announcing deployment of the US Terminal High Altitude Area Defense (THAAD) system -- a move which sparked domestic protests as well as complaints from China.

"I urge the North Korean government to immediately stop all provocations and threats targeting South Korea as well as the development of weapons of mass destruction," said President Park Geun-Hye in a televised Liberation Day speech.

Her comments came as both Koreas celebrated the anniversary of the peninsula's liberation from Japanese colonial rule in 1945.

Stressing that "true liberation" would involve reunification of the peninsula, Park said that could only happen by removing the fear of nuclear weapons, missiles and war.

She also warned the North that all attempts to provoke and intimidate the South would be counter-productive.

"The more efforts (the North) makes, the deeper the country's isolation in the international community will be and the bigger its economic problems will be," she said

The North's nuclear test in January resulted in a substantial strengthening of UN sanctions, but a defiant Pyongyang doubled down with a series of ballistic missile tests also banned by UN resolutions.

Tensions are expected to rise again when the South launches an annual joint military exercise with the United States later this month.

The planned missile shield has been condemned not only by Pyongyang but also Beijing, which views the deployment as a US move against its own national security interests and a threat to regional stability.

"The deployment of THAAD is an act of self-defence," Park said in her speech, adding that her priority as president was to "protect the lives of our people from the reckless provocations of the North".

THAAD has also hit domestic opposition, particularly from those living in the rural county of Seongju where the first battery will be installed.

Residents say the system's powerful radar will pose health and environmental hazards and argue that its presence will make them a target.

On Monday more than 900 Seongju residents had their heads shaved, a symbol of protest and determination.

"We need to show our determination in order to stop THAAD!" the protesters chanted as men and women, some in tears, had their heads shaved at a local park.

Some opposition lawmakers have sided with the residents and called for the deployment to be scrapped, a stance criticised by Park.

"I believe that such a matter ... should not be the subject of a political fight," she said.

"If there is any other way to protect our people and the country, one should propose an alternative," Park added.