Abdellatif Khaloul, an eye witness, told Reuters that "firefighters got there within half an hour but didn't find enough water to stop the blaze".
"I heard that many factory workers were trapped on the upper floors and cried from the windows for help."
Parts of the factory were still smoking early evening as rescue workers searched the charred remains for more bodies, he said.
Moustapha Taouil of the Casablanca civil protection service said "the lack of equipment maintenance" - involving an electric saw in particular - had led to the fire.
He said that entrance points to the Rosamor furniture plant been blocked, with an apparent view to preventing staff from stealing factory materials.
"We have been able to assess the total absence of security measures that ought to have been put into place by factory management," he said.
A security source also said on Saturday that windows at the factory had been fitted with iron bars, making escape difficult for those trapped inside.
Another official at the scene said that Adil Moufarreh, the factory owner, and his son Abdelali Moufarreh, who was the manager, were in police custody.
An official statement had earlier cited the presence of chemical products in the factory as being responsible for accelerating the fire.
"The fire spread rapidly throughout the factory because of the nature of the chemical products stored there," MAP said.
Inquiry opened
Firefighters battled the flames for three hours.
Officials from the prosecutors office visited the scene as part of an investigation to establish the cause of the blaze and any responsibility, MAP said.
Local officials also rushed to the scene to help supervise rescue operations, it said.
Survivors and relatives of the victims sais that working conditions and safety precautions at the factory were poor.
"The owner was more worried about protecting his mattresses and his material than the lives of his workers," Fawza Badr, 70, who lost her 20-year-old daughter Hadida, said.
The father of Abdelazziz Darif, 19, who died in the blaze, said his son "was paid the meagre sum of 250 dirhams (20 euros) a week and had no social cover."
The bustling coastal city of Casablanca is Morocco's leading port and the economic capital of this North African country.
It reflects the contrasts of Morocco, the westernmost Muslim country, with its rich modernity and poor, crowded neighborhoods with soaring unemployment.