Several thousand South Koreans staged an angry protest Thursday against the planned deployment of a US anti-missile system near their hometown, but President Park Geun-Hye insisted the move was a national security imperative.

South Korea's defence ministry announced last week the Terminal High Altitude Area Defence system, or THAAD, will be installed in Seongju -- a rural county about 200 kilometers (135 miles) southeast of Seoul -- by the end of next year.

The decision was predicated on the growing threat posed by North Korea's advancing nuclear weapons and ballistic missile programme.

But Seongju residents say the THAAD deployment makes their county a strategic target and complain that it carries health and environmental hazards.

"Let's block the deployment of THAAD, a threat to peace on the Korean peninsula!" chanted some 2,000 protestors, waving flags and banners that read 'No THAAD' as they sat outside Seoul station on Thursday.

The protestors were surrounded by hundreds of police, amid concerns of a repetition of a violent standoff last Friday, which saw Prime Minister Hwang Kyo-Ahn pelted with eggs and water bottles.

Hwang had been in Seongju to try and appease the residents, but ended up being trapped in his minivan for hours.

Thursday's protest began just hours after Park urged public support for THAAD.

"The government's decision ... was based on the judgement that it was the best way to protect our country and people from North Korean threats," Park said during a National Security Council meeting Thursday.

"If there is a better way...please let me know," Park added.

Tensions on the divided Korean peninsula have been running high since Pyongyang carried out its fourth nuclear test in January, followed by a series of ballistic missile tests.

On Tuesday, the North fired three ballistic missiles into the Sea of Japan (East Sea) in an exercise aimed at simulating pre-emptive attacks on South Korean ports and airfields hosting US military "hardware".