A fire that broke out in a building housing workers in the city of Mangaf in southern Kuwait early on Wednesday has killed at least 41 people, the country's deputy prime minister Sheikh Fahad Yusuf Saud Al-Sabah said during a visit to the site.

The deputy PM accused real estate owners of violations and greed, saying those factors contributed towards the incident.

"Unfortunately, the greed of real estate owners is what leads to these matters," said Sheikh Fahad, who also runs the interior and defense ministries.

The fire was reported to authorities at 6am local time, Major General Eid Rashed Hamad said.

"The building in which the fire occurred was used to house workers, and there was a large number of workers there. Dozens were rescued, but unfortunately there were many deaths as a result of inhaling smoke from the fire," another senior police commander told state TV.

"We always alert and warn against" cramming too many workers into housing accommodation, he said, without providing details on the workers' type of employment or place of origin.

The fire was contained and authorities were investigating its cause, officials said. (Reuters)