South Korea granted nurses new powers and legal protections Tuesday, and launched an investigation into a patient's death, as hospital chaos caused by striking trainee doctors entered a second week.

Major hospitals are struggling to provide services after thousands of junior medics handed in their resignations and stopped working last week to protest against government plans to sharply increase medical school admissions in the face of a rapidly ageing society.

The government said Tuesday it would launch an investigation after a patient died of a cardiac arrest in an ambulance after struggling to find a hospital.

Emergency services contacted seven different hospitals but "were told there were no trainee doctors", the daily JoongAng Ilbo reported.

"The government is conducting an on-site probe with related agencies into the death," Health Minister Cho Kyoo-hong said.

The mass work stoppage has also resulted in cancellations and postponements of surgeries for cancer patients and C-sections for pregnant women, with the government raising its public health alert to the highest level.

Nurses will now be allowed to perform some medical procedures previously reserved for doctors, and offered immunity from potential lawsuits linked to their new scope of work, Second Vice Health Minister Park Min-soo said.

"This pilot programme will legally protect the nurses who are filling the medical vacuum created by trainee doctors' walkouts at hospitals," Park said.

The government said it needed to protect nurses because there were currently some "grey areas" about what medical treatments could be performed by particular staff, at a time when nurses were "shouldering the workload" due to the strike.

Each hospital's administrators can work with nurses to decide which tasks they can perform.

The government has set a Thursday ultimatum for doctors to return to work, saying that legal action -- including prosecution and the suspension of medical licences -- will be taken against those who refuse.

"We urge the trainee doctors to return to medical fields as soon as possible," Park said.

- Nurse fears -

Nurses told AFP that the changes did not offer enough protection to them in life-or-death cases.

"Although it is claimed that legal protection is provided, I do not find it specific enough to feel safe," said Lee Hye-ok, a nurse at one of the five biggest hospitals in South Korea.

"Legal protective measures need to be much more specific and comprehensive."

Other nurses said they had no option but to perform certain tasks if no doctors were working.

"We nurses cannot refuse when they are told to help the patient on the spot when there is no one else available," said Park Na-rae, a nurse and union member of the Seoul National University Hospital.

"The worrying part is whether they will be held accountable if the patient's condition worsens."

- 'Destroy medical care' -

Doctors are restricted from strikes by South Korean law but the medics have said they have no option but to stop working to show their fierce opposition to the government's plan.

The Korean Intern Resident Association said in a social media post Tuesday they believed the medical reforms would "destroy medical care".

South Korean President Yoon Suk Yeol said Tuesday "medical reform cannot be subject to negotiation or compromise".

"No reasons can justify acts that hold lives and health of the people hostage," he said at a meeting.

Polls suggest up to 75 percent of the South Korean public supports the increase in medical school admissions.

Seoul says it has one of the lowest doctor-to-population ratios among developed countries and the government is pushing hard to admit 2,000 more students to medical schools annually from next year.

Junior doctors say the reforms are the final straw in a profession where they already struggle with tough working conditions.