US troops began delivering a missile defence system that has infuriated China to a deployment site in South Korea Wednesday, 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. It has imposed a host of measures seen as economic retaliation against the South, including a ban on tour groups.
TV footage showed large trailers in camouflage paint carrying what appeared to be missile-related equipment entering a golf course in the southern county of Seongju on Wednesday morning.
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 hospitalized, activists said.
Seoul's defence ministry said Wednesday's move was aimed at "securing operational capability of the THAAD as soon as possible", with a goal of fully installing the batteries by the end of this year.
The South 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 expressing ambivalence 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".
"This move has shut off any room for policy considerations by the next government and it is very improper," he said.
The South's tourist industry has been hammered by Beijing's boycott over THAAD, with Chinese visitor numbers -- normally more than half the total -- plummeting 40 percent last month even though the ban only came into force on March 15.
Retail conglomerate Lotte -- which provided the Seongju golf course site to the Seoul government -- has also been targeted, with 85 of its 99 stores in China shut down.
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 led by the USS Carl Vinson to the peninsula in a show of force, amid signs the North could be preparing for a sixth nuclear test.
The impoverished, isolated state says it needs nuclear weapons to defend itself against the threat of invasion, and has issued blood-curdling promises of retaliation in the event of an atomic strike against it.
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 joint drill involved artillery firing as well as torpedo attacks by submarines, state-run KCNA said, and demonstrated the country's determination to a "pour merciless rain of fire on the reckless imperialist US and its dirty followers", it said.
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.
It is also concerned that a regime collapse could trigger a flood of refugees across the border, and leave the US military on its doorstep in a unified Korea.
Chinese President Xi Jinping called Monday for "restraint" regarding North Korea in a telephone conversation with Trump.
US defence leaders and other top officials are to give a classified briefing on North Korea to all senators in an unusual meeting at the White House later Wednesday.