euronews/Chinese police detained four construction workers on Tuesday in connection with a fire that gutted a Shanghai skyscraper, killing at least 53 people and hospitalising more than 70.

Officials told state media that the four were welders operating without the correct permit.

The 28-storey building had been undergoing renovations when it caught fire early at 7:00 CET on Monday.

More than 70 people remain in hospital. Doctors said 17 of them are in a critical condition.

Resident Du Deyuan said his apartment on the 26th floor appeared to be intact but he criticised authorities for being too slow in responding to the emergency.

"The fire fighting and rescue measures were not sufficient. The operation took too long. I feel very disappointed," he told Reuters.

Concerns have been raised over why firemen took four and half hours to extinguish the flames.

But Shanghai city hall have rejected the criticism.

It said 25 fire units and more than 100 fire engines were at the scene yesterday.

China's rapid urban growth is throwing up vast numbers of new high-rise buildings.

While major fire disasters have been relatively rare compared to other developing countries, safety maintenance can be lacking.