More than 6,400 trainee doctors have submitted their resignations in protest of the government's plan to boost the number of medical students, officials said Tuesday, as worries mount that their collective action could put public health at risk.

Second Vice Health Minister Park Min-soo told reporters that the ministry ordered 757 trainee doctors to return to work, with tensions between doctors and the government spiking over the plan to add 2,000 to the country's medical school enrollment quota next year.

As of Monday, 6,415 trainee doctors at 100 hospitals submitted their resignations, with about 1,600 of them walking off the job, Park said.

There are around 13,000 trainee doctors in South Korea.

With trainee doctors stopping work at some hospitals, some patients have already experienced delays in surgeries and other treatments. Still, no major disruption in medical services has yet occurred.

To cope with a potential disruption of medical services, the government will extend operating hours at 97 public hospitals and emergency rooms at 12 military hospitals will be opened to the public, Park said.

The government says the increase in the admission quota is needed to address a shortage of doctors, particularly in rural areas and essential medical fields, such as high-risk surgeries, pediatrics, obstetrics and emergency medicine.

The number of doctors in South Korea relative to the size of the population is among the lowest in the developed world, according to health authorities.

But doctors have claimed that the government has not had full consultations on the matter and that the move will compromise the quality of medical education and services.

On Monday, the government took steps to suspend the medical licenses of two officials of the Korea Medical Association, which represents doctors.

If the two officials turn out to be urging doctors to join the collective action, their licenses will be cancelled, according to government officials.

Concerns about a vacuum in medical services have already become a reality for some, as trainee doctors at Severance Hospital declared the suspension of their service on the day, prompting the hospital to go into emergency mode and adjust the schedules of surgeries and procedures for patients.