The tranquility of a village set deep in the mountains in South Korea was shattered early on Wednesday morning with the sudden arrival of parts for a US missile defence system designed to thwart an attack by the North.

The Terminal High-Altitude Area Defence system, or Thaad, is being rushed into deployment at the site of an old golf course in Seongju amid growing tensions over Pyongyang’s nuclear and missile programmes.

The earlier-than-expected move prompted protests by hundreds of local residents and was denounced by the favourite to win South Korea’s presidential election on 9 May.

The US and South Korea agreed last year to deploy Thaad, which comprises radar, interceptor missiles and launchers that, theoretically, can strike incoming missiles in mid-flight.

The move has angered China, which says the advanced system will do little to deter the North while destabilising the regional security balance.

South Korea’s defence ministry said some elements of Thaad had been moved to a site on what had been a golf course in the south of the country, the route kept clear by large number of police officers, some carrying riot shields.

“South Korea and the United States have been working to secure an early operational capability of the Thaad system in response to North Korea’s advancing nuclear and missile threat,” the ministry said in a statement. The battery was expected to be operational by the end of the year, it added.

Television footage showed military trailers carrying large units, including what appeared to be launch canisters, being driven on to the site. Images showed protesters hurling water bottles at the vehicles and police trying to block them.

Late on Wednesday afternoon, thousands of police lined the single road leading to the entrance of the site, vastly outnumbering the hundreds of mainly older, local protesters who had been joined during the day by union and political activists from other parts of the country.

Baek-Gwang-soon, 73, who has lived in Seongju all her life, said she had been “speechless with anger” when the equipment arrived under cover of darkness.

“This is a quiet place, where we welcome outsiders with open arms,” Baek told the Guardian. “Now it’s being ruined by the arrival of American weapons that have turned us into a North Korean target.” Baek was holding a sign that read: “Is South Korea really a sovereign country?”

South Korean media reported that six launchers, several intercept missiles and at least one radar had been deployed in the area, where farmers say electromagnetic waves from the system’s radar pose a threat to public health and their melon crops.

The Pentagon said the deployment was a critical measure to defend South Korea and its allies against North Korean missile threats and it would be completed “as soon as feasible”.

The US and South Korean militaries have been reluctant to publicly discuss the progress of the deployment ahead of the South Korean presidential election.

Moon Jae-in, the frontrunner in the race, has said the new South Korean administration should decide on whether to deploy Thaad after gathering public opinions and having further discussions with Washington.

A spokesman for Moon said the decision to press ahead “ignored public opinion and due process”, and he demanded the deployment be suspended until the next administration was in place and had made its policy decision.

More than 10 protesters were injured during clashes with police. Kim Jong-kyung, co-head of a group of villagers protesting against the Thaad deployment, told Reuters some of them had sustained bone fractures. Kim said about 200 protesters, mostly residents in two towns near the battery site, rallied overnight and would remain near the location.

“We will continue our fight and there’s still time for Thaad to be actually up and running so we will fight until equipment is withdrawn from the site and ask South Korea’s new government to reconsider the plan,” Kim told Reuters by telephone.

A police official in Seongju, a town where Thaad is located, said police had pulled out from the location, and he was unaware of the reports of injuries.

Washington and Pyongyang have been ratcheting up pressure on each other in recent weeks, with the US sending an aircraft carrier group and nuclear submarine to the region and North Korea attempting more missile launches in defiance of layers of UN sanctions.

The Trump administration called the entire US Senate to the White House on Wednesday to be briefed by senior administration officials about the brewing confrontation. The unusual briefing underlines the urgency with which the Trump administration is treating the threat posed by Pyongyang’s continuing development of nuclear weapons and missile technology.

On Friday the US secretary of state, Rex Tillerson, is due to chair a UN security council foreign ministers’ meeting on the issue in New York, at which the State Department said he would call once more for the full implementation of existing UN sanctions or new measures in the event of further nuclear or missile tests.

North Korea’s KCNA news agency said on Wednesday that the country’s leader, Kim Jong-un, had supervised its “largest ever” live-fire drill to mark the 85th founding anniversary of its military, with more than 300 large-calibre, self-propelled artillery guns demonstrating their firepower at an event on the east coast.

The drill came instead of a nuclear test or the launch of a long-range missile. which had been feared, amid pressure from the US and China, North Korea’s sole major ally, which has been irritated by Pyongyang’s weapons development.

“The brave artillerymen mercilessly and satisfactorily hit the targets and the gunshots were very correct,” Kim said, adding that they “showed well the volley of gunfire of our a-match-for-a-hundred artillery force giving merciless punishment to the hostile forces”, according to KCNA.

A US submarine designed to carry 150 Tomahawk cruise missiles entered a South Korean port on Tuesday as the USS Carl Vinson carrier group steamed towards Korean waters in an effort to deter the North from a sixth nuclear test and more missile launches.

South Korea’s navy has said it plans to hold a joint drill with the US strike group in late April.

Donald Trump has vowed to prevent the North from being able to hit the US with a nuclear missile and has said all options are on the table.

The US began moving the first elements of the advanced missile defence system into South Korea in early March after the North test-launched four ballistic missiles.

Seoul and Washington say the sole purpose of Thaad is to defend against North Korean missiles, but China is concerned the system’s powerful radar can penetrate its territory and undermine its security.

South Korea accuses China of discriminating against some South Korean companies operating in China because of the Thaad deployment.