A blaze engulfed a downtown high-rise residential building, killing at least 49 people and injuring 90.

The fire broke out at 1:45 pm in one of three buildings under renovation near a busy intersection in downtown Shanghai. More than 60 fire engines were involved in battling the fire, which was brought under control about five hours after it started.

Twenty ambulances were called to the scene and three helicopters were also involved trying to rescue trapped residents.

More than 100 residents were saved by firefighters.

Gas and electricity supplies in the area were cut off to reduce the risk of explosions or further fires.

One witness who works in a nearby private company said: "I saw at least four or five people hanging onto the scaffolding which covers the building, screaming for help. Firefighters were trying to get closer and use their hoses to cool a path on the scaffolding so that they could climb down and escape.

"A helicopter arrived at around 4:00 pm, trying to rescue people from the top of building but failed because of the intense smoke.”

The sound of small explosions was heard about four hours after the fire broke out. The 28-floor building was undergoing renovation and was covered with flammable safety netting, to prevent tools or masonry falling onto the street, which made it more difficult for firefighters.

Dong Qilin from Pengpu Fire Brigade said: "We tried to approach the building from all angles available, including from the nearest building."

Unlike commercial skyscrapers that have fire-prevention systems, residential buildings are not so well-equipped. The cause of the blaze is still under investigation.