SEOUL -- South Korea's health minister said on Monday authorities will start inspecting hospitals in order to take legal action against trainee doctors who have ignored an ultimatum to end a walkout over government plans to increase medical school admissions.

Around 9,000 resident and intern doctors, or about 70% of the country's total, have walked off the job since Feb. 20, leading to the cancellation of some surgeries and treatments and straining emergency departments.

The government had warned the protesting trainee physicians they could face administrative and legal penalties, including the suspension of their medical licences and fines or a jail term if they did not return to work the end of last month.

"From today, we plan to conduct on-site inspections to confirm trainee doctors who have not returned, and take action according to the law and principle without exception," Health Minister Cho Kyoo-hong told a televised briefing.

"Please keep in mind that doctors who have not returned may experience serious problems in their personal career path."

For protesting doctors who returned to the field, Choo said the government would consider extenuating circumstances when contemplating any action against them.

Later, Vice Health Minister Park Min-soo told a briefing that the government would take steps to suspend the medical licences of some 7,000 trainee doctors who had left their jobs.

Up to now, there has been little sign of either side backing down. Thousands of South Korean doctors held a mass rally on Sunday organised by the Korean Medical Association (KMA), which represents private practitioners, defying official calls for the trainee physicians to return to work.

The World Medical Association, a group representing physicians, said in a statement on Sunday it "strongly condemns the actions of the Korean Government in attempting to stifle the voices of elected leaders within the Korean Medical Association," adding it affirmed the right of doctors to collective action, including strikes.

The young doctors who are protesting say the government should first address pay and working conditions before trying to increase the number of physicians.

The government says the plan to increase the number of students admitted to medical schools by 2,000 starting in the 2025 academic is needed in a rapidly ageing society with one of the lowest numbers of doctors to patients ratios in developed economies of 2.6 doctors per 1,000 people.

The plan to boost medical school admissions is popular with the public, with about 76% of respondents in favour, regardless of political affiliation, a recent Gallup Korea poll found.

Some critics, however, accuse President Yoon Suk Yeol's government of not consulting enough and of picking a fight over the issue ahead of parliamentary elections in April.