At least 37 people have been killed and more than 125 injured in a fire at a hospital in South Korea which mostly cares for elderly people.

Key points: Fire at Sejong Hospital believed to have started in a first-floor emergency room

Fire at Sejong Hospital believed to have started in a first-floor emergency room More than 190 patients were in the hospital when the blaze broke out

More than 190 patients were in the hospital when the blaze broke out The cause of the fire is not known

The blaze broke out at the Sejong Hospital in the city of Miryang, about 270 kilometres south-east of Seoul, around 7.30am (local time).

A total of 194 people had been hospitalised in two buildings of the hospital — the general medical ward and its nursing ward for the elderly.

The blaze began at the general ward's first-floor emergency room and most of the dead were from the first and second floors, the National Fire Agency official said.

The death toll had previously been reported as higher by the National Fire Agency who later said the misstep had happed because of double counting.

But officials said fatality numbers were still expected to rise further with at least 14 of the injured in a critical condition.

A firefighter inspects the burnt hospital in Miryang after the deadly fire. ( AP: Kim Dong-mi/Yonhap )

The cause of the fire was not immediately determined.

Miryang fire officials put out the blaze around three hours after it started and preventing it from reaching the upper floors.

Most of the 37 deaths appeared to be due to suffocation, with only one suffering burns, said an agency official who spoke on condition of anonymity because he was not authorised to speak to media.

The identification of the dead was underway, he said.

Television reports showed black smoke billowing from the windows and entrance to the hospital and flames flickering.

A person is carried from the hospital fire ( AP: Kim Dong-mi/Yonhap )

The hospital's operations were suspended after the fire.

President Moon Jae-in convened an emergency meeting with senior advisers and expressed regret over the blaze.

He ordered officials to provide necessary medical supports to those rescued, find the exact cause of the fire and work out measures to prevent future fires, according to his spokesman Park Su-hyun.

Several recent fires in South Korea have been deadly.

In late December, 29 people were killed in a building fire in central Seoul, which was the country's deadliest blaze over the past decade before the hospital fire.

Last weekend, a fire at a Seoul motel killed six people, and police arrested a man who allegedly set it ablaze in anger because he had been denied a room for being heavily drunk.

In 2014, a fire set by an 81-year-old dementia patient killed 21 at another hospital for the elderly.

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Reuters/AP