The death toll from a fire at a Beijing hospital grew to 29 on Wednesday, the Chinese capital’s biggest in at least two decades, killing 26 patients and injuring scores.

After the fire broke out at Changfeng Hospital on Tuesday, individuals used knotted bed sheets to scale down the walls to escape the smoke and flames.

According to Reuters witnesses, broken and burned out windows could be seen at the scene, where there were several police officers, some in plain clothes.

All but three of the 29 dead were patients, officials told a media briefing on Wednesday, with the fire having been put out in half an hour.

“There was a lot of smoke, I could see it,” said an elderly local resident who gave only his surname, Li. He gave Reuters video clips he took of smoke billowing from the upper floors of the hospital.

Authorities are investigating Beijing’s deadliest fire since at least 2002, when a blaze at an internet cafe killed 25.

Initial checks showed the fire, which mostly affected a wing for critically ill patients, was caused by inflammable painting material at a ward under renovation, the officials said.

By Wednesday, many social media posts critical about the fire on WeChat had been either censored or deleted, Reuters checks showed.

“Rescue work at the scene concluded in 3-1/2 hours, but the public only knew that 21 had died from the fire when it was already past eight in the evening,” one person wrote in a WeChat post subsequently deleted.

“It is very puzzling that little information was known about a fire killing 21 people in a densely populated major city like Beijing before the official notification.”

Early on Wednesday, 39 injured were still in hospital, three in critical condition, and 18 serious, the officials told the briefing.