Portland firefighters responded to a fire Friday morning in a stairwell of 22 Smith St. in Portland’s East End.

The fire started about 4:30 a.m. on the third floor stairwell landing outside an apartment, fire officials said.

Firefighters put out the fire before it spread from the enclosed stairwell to the interior of the apartment, said Deputy Fire Chief Keith Gautreau.

The cause remains under investigation, although there is nothing to indicate it is suspicious, he said. Nobody was injured.

The second floor was vacant and everybody on the third floor and first floors got out of the building, he said.