It seems a cigarette could have triggered the fatal fire.

(Keystone)

The four adults and two children who died in a Swiss house fire have been identified as asylum seekers from Ethiopia and Eritrea.

Early on Monday morning, a fire broke out in one of the lower floors of an apartment building in the city of Solothurn in northwestern Switzerland. Six people died and several others required hospital care.

+ Dozens of rescue workers rushed to the scene

Local authorities say the fire was caused by improper handling of tobacco products, reported Swiss public television, SRF, on Tuesday.

One person has been arrested in connection with the fire and a criminal investigation is underway on multiple counts of negligence causing death, bodily injury and the fire.

A woman and baby were found outside the building, suggesting they might have jumped out a window to escape the fire and smoke that had filled the upper floors of the four-storey building. The baby survived but the woman died.

Investigators are also looking into why there were 20 people in the building when only nine were registered as living there.