The blast at 12:10pm (0410 GMT) was triggered by a suspected gas leak and brought down a neighbourhood committee building housing a canteen, trapping more than 20 people, state news agency Xinhua said.
As of 7pm, 15 people had been pulled from the rubble, six of whom had lost their lives.
Rescuers are attempting to free another 11 people trapped in the rubble, Xinhua said.
Rescue efforts continued Friday night, with videos and photos from Xinhua showing orange-clad workers in hard hats climbing through the rubble under floodlights.
Some of the injured people have been taken to hospital for treatment, Xinhua reported, without giving further details of their condition.
Footage posted by state broadcaster CCTV on social media showed smoke and dust billowing from the collapsed building in Wulong district on the outskirts of the southwestern megacity.
The scene of the blast appeared to be in the middle of other buildings and was surrounded by a crowd of bystanders.
Another clip by Xinhua showed dozens of rescuers in military fatigues jogging along a road to the site carrying shovels over their shoulders.
More than 150 fire and rescue workers have been deployed to the site, CCTV said.
Heavy lifting and excavation equipment have also been sent to the scene.
The cause of the blast remains under investigation.
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