Representatives of dozens of organizations, labor unions and social movements across South Korea took part in a massive mobilization in Seoul on Tuesday to reject U.S. President Donald Trump and the war he threatens on the Korean peninsula.

Protesters gathered in the historic center, Seoul's Joseon-era Gwanghwamun Square, to show their support for an independent foreign policy in which Koreans would be able to exercise sovereignty and determine matters of war and peace on the divided peninsula.

"We oppose the visit to South Korea by Trump, who has heightened the fears of war on the Korean Peninsula," said one of the protesters, reading from a statement.

More than 15,000 officers were deployed to provide security monitor the demonstrations, according to the National Police Agency. But despite the overwhelming police presence, thousands of protesters attempted to block Trump's entrance to Cheong Wa Dae, also known as the Blue House: the office of South Korean President Moon Jae-In.

Trump has caused significant anxiety among South Koreans from all walks of life with his casual talk of having to "totally destroy" North Korea, and other vaguely menacing statements such as “Sorry, but only one thing will work!"

On Twitter, the US president has labeled Moon's modestly pro-engagement approach to Pyongyang as "appeasement," a comment which outraged South Koreans.

"I came here to protest because I'm afraid of a war," one 37-year-old protester told The Washington Post. "And if a war breaks out, we all die."

In a recent letter from the Pentagon Joint Chiefs of Staff to two members of the U.S. House of Representatives, U.S. officials noted that any war on North Korea would endanger tens of thousands of civilians in Seoul, a densely populated city with 25 million residents.

Meanwhile, the far-right and militantly pro-U.S. Korea Freedom Federation reverently welcomed Trump's visit, describing it as a "God-like move" that would "instantly reverse" the fraught security situation in the region after the U.S. and its ally were forced on the "defensive" by North Korea's weapons tests.

Pyongyang responded to Trump's visit with a characteristically acidic salvo of statements, including an opinion piece published in the official Rodong Sinmun entitled “Foolhardy Acts of Warlike Maniacs."

"(The) tragedy is that Trump, accustomed to getting money by cajoling other people, recklessly mulls playing a nuclear war gambling while despising the opponent," they said. "The Trump group would be well advised to behave themselves after thinking twice about the catastrophic consequences of their reckless war hysteria."

South Korea is the second leg of the U.S. president's high-stakes Asian trip, which will also take him to China, Vietnam and the Philippines.