TEHRAN, Young Journalists Club (YJC) - Children were among the dead, police in the northwestern Swiss city of Solothurn said in a statement, without giving details.
Firefighters were investigating the cause of the fire.
A resident of the apartment noticed smoke in a stairwell and alerted authorities at about 0110 GMT, police said. There were about 20 people inside the building at the time, they said.
The fire likely broke out in the lower portion of the structure, causing it to fill with smoke that later billowed out of the windows. Dozens of firefighters and rescue personnel responded to the blaze.
A neighboring building was also evacuated as a precaution, authorities said, although its residents were later able to return to their apartments.