Assistant chief of the Drakenstein fire department Dereck Peceur said another 13 workers were hospitalised, some of them with second-degree burns.

The fire was the second this year at a plant owned by Naspers subsidiary Paarl Media.

In February a blaze destroyed a R200 million magazine printing press at Paarl Gravure in Cape Town's Montague Gardens, with no casualties.

Peceur said Friday's fire broke out at Paarl Print, in the Boland town's industrial area, shortly before 8am.

The building housed offices, printing equipment, a bindery and a storage area, and the workers who died were trapped inside.

The fire was under control just after 1pm, but it was still "extremely hot" inside the building, which had been gutted from end to end.

Fire-fighters from the adjacent Cape Winelands municipality had also been called in to help.

Peceur said he did not know at this stage how the fire started. The department would be able to investigate only once things had cooled down.

He was unable to confirm a rumour that it followed a gas leak in a staff canteen.

An employee at a nearby building told Sapa that the air in the vicinity of the blaze had been "so black and so thick with smoke it was difficult to breathe".

"Everyone's still standing around crying," she said.

Two were in a normal ward and five in the intensive care unit.

They were being treated for flash burns and inhalation wounds.

The burns ranged from minimal, to injuries covering 75 percent of their bodies, she said.

All the intensive care patients would go into theatre on Friday afternoon so doctors could clean their wounds under anaesthetic.

Paarl Media spokesperson Nelia Burger said it was not known at this stage how the fire started.

"There will be an investigation launched soon, obviously," she said.

The flames had spread "extremely quickly", and almost the whole factory was destroyed.

"We're still busy doing a head count to make sure who was on the shift," she said.

This was made more difficult by the fact that the computerised clocking-in records had been destroyed in the flames.

She said Paarl Print ran off books, diaries, short-run magazines, brochures and school textbooks, and did a lot of work for the government and other African countries.

Arrangements were being made to finish jobs at other plants.

According to the Paarl Media website, the plant offered an extensive flat sheet division, web facilities, book press and a state-of-the-art bindery.

The site says Paarl Print is 100 percent BEE compliant with a 36 percent black shareholding.

Sapa

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