At least 37 people are believed to have perished after the fire took hold of the four-storey NCCC Mall on Saturday morning in the southern city of Davao.
President Rodrigo Duterte, who is from the city, visited victims’ relatives outside the burning building on Saturday night.
He told them there was “zero” chance their family members had survived, witnesses said.
Flames were eventually brought under control early on Sunday morning but fire officials said they had not yet entered the section where they believed the missing were trapped.
The top floor was home to a 24-hour call centre for US multinational market research company SSI.
Retired seaman Jimmy Quimsing was waiting to hear about his 25-year-old son Jim Benedict who worked at the call centre and had not been in contact since the fire broke out.
He said he spoke to President Duterte who told him to prepare for the worst.
“He told us zero, no one would survive under these circumstances,” Mr Quimsing said.
Honeyfritz Alagano, Davao’s fire marshal, said the blaze may have started on the third floor in a furniture department.
He said: “One of our firemen here has a kid who is an (call centre) agent in there. He told us some of them went to collect their stuff at their lockers and were trapped.
“The mall is an enclosed space with no ventilation. When our firemen tried to enter they were pushed back by smoke and fire.”
There are few to no fire safety standards in the Philippines and massive fires are not uncommon.
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In 2015 72 people were killed in a slipper factory fire in Manila.
Survivors blamed barred windows and sweatshop conditions for trapping workers inside.