Thousands of doctors affiliated with the largest coalition of neighborhood practitioners in South Korea launched a full-scale, one-day strike on Tuesday, despite the government's return-to-work order and threat to disband the organization.

The Korean Medical Association, representing some 140,000 doctors, mostly self-employed practitioners, pleaded to the public that it is the "last chance" to salvage the nation's health care from the brink of collapse. Some 50,000 people were thought to have participated in a mass rally in Seoul's Yeouido, according to the KMA, while police estimated the figure to be between 5,000 and 12,000.

Vowing to be at the forefront of the battle against the government, Lim Hyun-taek, the KMA's head, said doctors will go on an indefinite strike starting June 27 if the government rejects their demands, warning that they will "fight to the end."

The KMA's three demands are: revisit from scratch the discussion on raising the medical school admissions quota; supplement key points in the government's policy package for essential medical services; and cancel all administrative orders and penalties against junior doctors who have walked off the job since February.

The government has rejected the demands.

"We doctors will fight to the end until the oppressive government treats doctors as valuable professionals who save lives, not as slaves. ... Let's unite to fight against the government's dictatorship and save the country's health care," Lim said during the rally in Yeouido Hangang Park in western Seoul.

Kim Chang-soo, who heads the Medical Professors Association of Korea, also said during the same rally that Tuesday's strike signaled the start of the medical circle's "fierce battle" against the government, adding that doctors will continually strive to inform the public about the medical reform's negative effects.

The KMA estimated that the walkout would be the biggest since 2000, when doctors protested the government's policy of separating the prescription and dispensing of drugs at the time, as 90.6 percent of its members -- including private practitioners and medical professors -- voted in favor of the walkout.

In an attempt to reduce any potential medical vacuum, the government ordered the doctors to return to work at 9 a.m., as some 4.02 percent of the nation's 36,371 private hospitals had reported to authorities their intention to close for the day. Each local government is to monitor whether the doctors under its jurisdiction participate in the mass closure, according to the Health Ministry.

President Yoon Suk Yeol condemned medical professionals, arguing that their actions could threaten patients' lives and health, as he urged them to engage in dialogue led by the presidential medical reform panel.

"Many people, including patients' groups and from all walks of life, are asking the medical circle to stop its collective action," Yoon said in a Cabinet meeting in his office in Seoul on Tuesday.

"Since the government has a responsibility to the lives and health of its citizens, it has no choice but to take strict action against illegal acts that abandon patients," he said.

In a separate briefing, Jun Byung-wang, policy chief at the Health Ministry, explained the government's argument that for private practices, taking the day off to participate in the rally amounts to an illegal refusal of treatment.

University hospitals continued to remain open to provide medical treatment.

If the closure rate of local clinics exceeds 30 percent, the government will conduct on-site inspections and gather evidence to take administrative measures such as suspending medical licenses in accordance with the law.

"The only way to resolve this issue is through engaging in constructive dialogue and rational discussions rather than engaging in actions that threaten the lives of patients," Health Minister Cho Kyoo-hong said in a government response meeting.

Cho noted that the government will seek to persuade the medical circle to end its collective refusal of treatment until the very end, and handle illegal acts sternly, warning that doctors would face legal punishment if they do not comply.

He also said the government has requested police investigations into social media posts encouraging participation in illegal collective action and refusing to provide medical services under the guise of voluntary participation.

Jun urged doctors to abide by their obligations to provide care to patients. "People's right to life is the most basic, fundamental right that must be protected under any circumstances," he told reporters.

Jun also threatened that the government could "dissolve" the KMA if it continues to engage in actions that go against the purpose of its establishment, which is to promote public health and welfare and advance medicine.

In addition, a nationwide federation of patient groups with severe diseases demanded that the government respond strictly to doctors who go against the Hippocratic oath by engaging in illegal activities.

"The government's lukewarm response has exacerbated the current situation. It should now fairly enforce the law on doctors and proceed with administrative action, such as by revoking their licenses," the federation said in a statement.

Yet despite the government threats and patient fear, no major disruptions to health care services were reported.

A senior official at Seoul St. Mary's Hospital, one of the nation's top institutions, told The Korea Herald that less than 10 percent of doctors there have walked out. Another official at Asan Medical Center in Seoul said that many professors who have decided to strike are still seeing patients.