South Korean police raided the offices of the Korean Medical Association on Friday, an officer told AFP, as the government contends with a doctors' strike that has led to chaos in hospitals.

Nearly 10,000 junior doctors -- about 80 percent of the trainee workforce -- walked off the job last week. They are protesting government plans to sharply increase medical school admissions to cope with shortages and an ageing society.

The government had set a Thursday deadline for medics to resume work or face potential legal consequences, including suspension of medical licenses and arrest.

There is currently no official data on the number of doctors who have returned post-deadline, the health ministry told AFP, but South Korea's Yonhap news agency said most striking doctors remained off the job on Friday.

The mass work stoppage has taken a toll on hospitals, prompting the government to raise its public health alert to the highest level.

Around half of the surgeries scheduled at 15 major hospitals have been cancelled since last week, according to the health ministry.

Under South Korean law, doctors are restricted from striking.

Earlier this week, the government requested police investigate people connected to the stoppage.

Seoul's police confirmed that it raided the Korean Medical Association (KMA) on Friday.

In response to the Thursday deadline and initiation of a police probe, the KMA slammed the government for "intimidation tactics" and accused it of turning the country into a "totalitarian state".

The government says it is trying to address one of the lowest doctor-to-population ratios among developed nations. It is pushing to admit 2,000 more students to medical schools annually from next year.

Doctors say the plan will hurt the quality of service and medical education, but proponents say medics are mainly concerned the changes could erode their salaries and social status.

The KMA said its members will hold a rally in Seoul on Sunday, with local reports saying around 25,000 expected to join.