According to the fire brigade, a powerful explosion preceded the fire and most of the factory building has collapsed.
At least four people have been killed in a fire at a biscuit factory in central Greece in one of the country's deadliest recent industrial accidents, officials said on Monday.
Six employees and a fireman have been hospitalised but are not believed to be in immediate danger, the health ministry said.
Television footage showed the gutted remains of the Violanta factory outside the city of Trikala, some 245 kilometres northwest of the capital Athens.
The fire broke out shortly before 4 am in a wing of the food production plant during the night shift, while 13 people were inside.
According to the fire brigade, a powerful explosion preceded the fire and most of the factory building has collapsed.
"Today, a serious incident occurred at our factory premises during the night shift, due to a cause that remains unknown at this time," the company said in a statement.
Greek Prime Minister Kyriakos Mitsotakis said, "A fire department team is already examining the causes of this tragedy so that we know exactly what happened and assign responsibility where it is due."
He told his cabinet the factory was a "modern" one and said the thoughts of the nation were with the families of the victims.
The Violanta plant, the company's first and biggest, produced 12,500 tonnes of biscuits, cookies and wafers per year, according to the company website.
The brand is among the fastest-growing in Greece, with a major presence in shops, and exports to around 40 countries.
The blaze is one of Greece's most fatal industrial accidents and one of the worst in several years.
In 1992, 15 people died in a refinery explosion in the industrial zone of Elefsina, near the port of Piraeus.