Patients’ relatives say they heard a blast and suspect an oxygen tank might have exploded.

A fire at a hospital in Taiwan‘s most populous city killed nine people and injured 15 others early on Monday.

The blaze broke out on the seventh floor of the building, which was used for hospice care, according to the New Taipei City Fire Department.

Media footage showed patients being wheeled out of the building in their hospital beds, while medical workers took others out on stretchers and into ambulances.

Fire Chief Huang Te-ching said the cause of the fire was still being investigated and denied reports that a sprinkler system malfunctioned.

“The sprinkler device was on but there’s some distance between its location and where the fire started so the fire couldn’t be immediately put out,” he told reporters.

Patients’ relatives said they heard a blast and suspected an oxygen tank might have exploded, causing the fire, local media reported.

Prime Minister William Lai said the health ministry was overseeing rescue efforts at the hospital in New Taipei City. He apologised to the public and expressed condolences over the tragedy.

“We will review the cause of the incident to prevent a similar situation from happening again,” said Lai.

President Tsai Ing-wen, on a stop-off in the United States on Monday on her way to visit two of Taiwan’s remaining diplomatic allies, Belize and Paraguay, expressed grief for the dead and hope for the injured, the government said.