The 28-story building in the Jing’an District of the Chinese city was being renovated when a fire broke out at 2 p.m. local time (1 a.m. ET), the state-run Xinhua News Agency reported.
A witness said building materials caught fire, then spread to scaffolding and then to the building, which housed many retired teachers, Xinhua reported.
The fire appeared to have been put out about six hours later, and firefighters could be seen removing bodies from the building.
The death toll was initially put at at least eight, but later Xinhua reported that 42 people had been killed.
Xinhua said 90 people rescued from the building had gone to nearby hospitals, but added that the true number of injured was not immediately known.
Update: ABC News reports that 53 people have now died from the blaze, and that welders working in the building have been detained in connection to the fire:
A preliminary investigation showed that four welders improperly operated their equipment, setting off Monday’s fire in Shanghai, the city government and state television reported.
Witnesses and building residents quoted earlier by state media said the blaze began when building materials caught fire. It then spread quickly to scaffolding covering the 28-story building, which houses a number of retired teachers as well as other families.
In addition to the 53 fatalities, the city government said Tuesday that more than 70 other people had been rushed to hospitals. Deputy Mayor Shen Jun said 17 were in critical condition.