US troops began delivering a missile defence system that has infuriated China to a deployment site in South Korea, amid heightened tensions over the North's nuclear ambitions.
Washington is urging Beijing -- Pyongyang's sole major ally -- to do more to rein it in, but the Asian giant has reacted with fury to the planned installation of the Terminal High Altitude Area Defense (THAAD) system.
The US and ally South Korea say its deployment, agreed last year, is intended to guard against missile threats from the nuclear-armed North.
But China fears it will weaken its own ballistic capabilities and says it upsets the regional security balance.
TV footage Wednesday showed large trailers in camouflage paint carrying what appeared to be missile-related equipment entering a former golf course in the southern county of Seongju on Wednesday morning.
THAAD "will be operational in the coming days and able to better defend South Korea against the growing North Korean threat," Admiral Harry Harris, who heads Pacific Command, told lawmakers in Washington.
Hundreds of residents -- who are concerned over the potential environmental impact -- protested angrily, some clashing with police. More than 10 were injured including three who were hospitalised, activists said.
Seoul's defence ministry said the aim was "securing operational capability of the THAAD as soon as possible", with a goal of fully installing the batteries by the end of this year.
South Korea is holding a presidential election next month to choose a successor to ousted leader Park Geun-Hye, and Seoul and Washington are pressing ahead with the deployment with some candidates ambivalent over the system -- including front-runner Moon Jae-In, of the left-leaning Democratic Party.
His spokesman Park Kwang-On expressed "strong regret" at the delivery, saying it ignored "required procedures".
Beijing condemned the move, with foreign ministry spokesman Geng Shuang telling reporters the THAAD deployment "severely undermines China's strategic security interests".
"It helps in no way to achieve the denuclearisation of the peninsula and regional peace and stability," he said, adding China would "take necessary measures to safeguard its own interests".
Beijing has imposed a host of measures seen as economic retaliation against the South, including a ban on tour groups.
- 'Rain of fire' -
THAAD is designed to intercept and destroy short and medium-range ballistic missiles during their final phase of flight.
The latest move comes as tension soars on the Korean peninsula following a series of missile launches by the North and warnings from the administration of US President Donald Trump that military action was an "option on the table".
Washington has deployed an aircraft carrier strike group to the peninsula in a show of force, amid signs the North could be preparing for a sixth nuclear test.
In Pyongyang's latest display, leader Kim Jong-Un oversaw the country's largest-ever firing drill to mark the founding anniversary of its military, state-run media said Wednesday.
The drill saw more than 300 large-calibre self-propelled guns firing simultaneously and torpedo attacks by submarines, state-run KCNA said, demonstrating North Korea's determination to pour a "merciless rain of fire on the reckless imperialist US and its dirty followers".
Seoul held a large annual drill of its own Wednesday, involving some 100 artillery pieces, 90 armoured vehicles and 50 aircraft, as well as 2,000 South Korean and US troops, the defence ministry said.
Speaking in Berlin, China's Foreign Minister Wang Yi urged an end to US-South Korean military manoeuvres to calm tensions on the peninsula.
The US has long pushed for China to make more efforts to curb Pyongyang's behaviour.
But Beijing says it has less sway over its wayward neighbour than Washington believes.
After briefing senators in a highly unusual meeting on Wednesday at the White House, Pentagon chief Jim Mattis, Secretary of State Rex Tillerson and Director of National Intelligence Dan Coats issued a statement that toned down military rhetoric.
The statement said the US wants to bring North Korea back to the "path of dialogue" and would use diplomatic measures and additional sanctions to increase pressure on the regime.