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 percent of the country's total, have walked off the job since February 20, leading to the cancellation of some surgeries and treatments and putting a strain on emergency departments.

The government had warned the protesting trainee physicians they could face administrative and legal penalties, including the suspension of their medical licenses and fines or a jail term if they did not return to work by 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, Cho said the government would consider extenuating circumstances when contemplating any action against them.

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

Patients outside a major hospital in Seoul told Reuters they were concerned about the impact of a drawn-out standoff on the administration treatment and called for talks to ensure a swift resolution.

"Doctors should first return and reassure patients and their families and then have a dialogue with the government," said a patient, who only gave her surname as Song.

Lee Hye-ji, a 37-year-old renal dialysis patient, said she was worried about what would happen if her condition deteriorated.

"I would be extremely anxious if I ever need to undergo a kidney transplant surgery, but there are no doctors available."