Image copyright The Washington Post/Getty Image caption Fire officials believe the blaze began in the roof of the senior community building

A 74-year-old man has been found alive and in good spirits five days after a fire broke out at his assisted-living complex in Washington DC.

Workers found him inside his apartment on Monday morning, where he is believed to have been trapped since Wednesday.

More than 100 senior residents were evacuated, but it was believed everyone had been accounted for, according to Mayor Muriel Bowser.

She said the man was taken to hospital for non-life threatening injuries.

Workers were checking the structural integrity of the building, which had collapsed in parts, when they heard the man shout out.

"He had a sense of humour," structural engineer Allyn Kilsheimer told reporters Monday. "When I said, 'We're coming to get you,' he said, 'I'm not going any place.'"

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They then forced open the man's apartment door, to find him sitting on his couch, officials said.

Mayor Bowser said: "The workers helped him into a chair and out of the building." He has not been named.

Fire officials believe last week's fire broke out in the attic of the Arthur Capper Senior Housing Center.

Ten people were injured and a huge plume of black smoke was sent into the air.

Residents complained that they did not hear any alarms after the fire started. Instead, residents were alerted by US Marines and neighbours who banged on their doors.

Bruce DarConte was one of those neighbours, and he told local media: "As we saw the fire alarms, we were pulling them - nothing. So we just kept going. It didn't pay for us to stand there."

Mayor Bowser said an investigation is underway to determine how the man was missed by both fire fighters who conducted searches in the building and a management company.

"We are rechecking to assure that [all residents] are accounted for," she said.

Fire officials are also investigating the reports that fire alarms at the building were not working.