Mexico City's Civil Protection chief Fausto Lugo said rescuers were using dogs and specialized equipment to look for workers still trapped beneath the rubble but they needed to proceed "with a lot of care to not put at risk" their colleagues and any survivors.
The accident took place in what was to be the multistory parking garage of a shopping center in Mexico City's Olivar de Los Padres district.
A statement from the government of Mexico's capital said initial reports indicated the collapse came when a beam being raised by a crane struck a support column.
The nine injured have been transferred to hospitals, authorities said.
Lugo raised the death toll by one to six late Monday.
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