North Korea on Wednesday labelled South Korean President Park Geun-Hye a "psychopath" after she made a speech slamming Pyongyang's nuclear ambitions and defending the deployment of a US anti-missile system.

In her televised address on Monday, Park had stressed that deploying the Terminal High Altitude Area Defense (THAAD) system was an act of "self-defence" in response to the North's expanding nuclear weapons programme.

A spokesman for the North's Committee for the Peaceful Reunification of the Country said Park's argument was "preposterous" and unfounded.

"This is just a lame excuse and she should know that no one will be taken in by such sophism of a puppet that can do nothing without an approval of her US master," the spokesman said.

"This is no more than nonsense talked by a psychopath," he added in a statement carried by the North's official KCNA news agency.

North Korea has threatened to take "physical action" against the THAAD deployment, saying any South Korean ports and airfields hosting US military hardware would become a target.

Beijing is also opposed to the move, seeing it as a US bid to flex its military muscle in the region and undermine China's own missile capabilities.

US Army Chief of Staff, General Mark Milley, addressed those concerns during talks on Tuesday with his Chinese counterpart, General Li Zuocheng in Beijing.

THAAD is "not a threat in any way to China," Milley told Li according to a US Army statement.

Deploying the system "is a defensive measure to protect South Koreans and Americans from the North Korean ballistic missile threat," he added.

Milley was due to hold talks with top South Korean military officials in Seoul on Wednesday.

The THAAD issue has also been a target of domestic criticism, particularly from those living in the rural South Korean county of Seongju where the first battery will be installed.

Several hundred protestors turned out in Seongju for a visit Wednesday by Defence Minister Han Min-Koo, who sought to ease concerns that the system's powerful radar will pose health and environmental hazards and make the district a military target.

Han began by apologising for the lack of prior notice regarding the planned deployment but stressed that defending the South against North Korean aggression was the ultimate priority.

"Please understand (the government's) desperate resolve to protect people's lives," he said.

More than 900 Seongju residents had their heads shaved on Monday as a mark of protest, and many of those were among the demonstrators who greeted Han with anti-THAAD slogans and demands to scrap the deployment.