Some of the seriously injured have been rushed to Thanjavur government hospital.
All the four labourers were working in the basement when one portion of the building collapsed.
No casualties were reported in the incident.
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The affected, a mix of flat owners and tenants, expressed immediate concern over finding new accommodation.
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A tragedy was averted as a five-story building evacuated by residents on Thursday afternoon after it developed cracks collapsed hours later.
In the incident, two teachers were also injured while the condition of six students was said to be critical.
There are more than 160 certified licensed structural engineers empaneled with the civic body.
Singh said that three persons were killed in the incident and six others injured, who have been rushed to Lucknow.
Most of the 20 migrant labourer women killed in Chennai were young mothers.
A total of 26 persons have been rescued so far as the non-stop rescue efforts.
Many of those feared trapped under the debris are believed to hail from Andhra Pradesh.
Police arrest five in connection with the Chennai building collapse and rescue efforts are still under way.
Of the three municipal corporations, the North corporation reports the most number of building collapses.