Thousands of South Korean doctors protested on Sunday in an escalating standoff with the government over medical training reforms, which has seen junior doctors quit en masse, plunging hospitals into chaos.

Reports have it that about 10 thousand junior doctors quit and stopped working nearly two weeks ago to protest hikes to medical school admissions from next year meant to combat shortages and an ageing society.

The striking professionals have defied a February 29 government deadline for them to return to work or face legal action, including possible arrests or suspensions of their medical licenses.

The protestors wore black masks and waved signs saying: "We oppose the medical school admissions increase".

The mass work stoppage has taken a toll on hospitals, with crucial treatments and surgeries cancelled, prompting the government to raise its public health alert to the highest level.

Under South Korean law, doctors are restricted from striking, and the government this week requested police investigate people connected to the stoppage.