A passer-by, who police said observed smoke billowing from the roof of a home in Lynbrook, was credited with helping save the occupants of that house Sunday — after he knocked on the door, alerting them to the danger.

Lynbrook police said there were at least three people home when the unidentified man saw smoke coming from the roof of the house on Scranton Avenue at about 5 p.m., stopped, knocked on the door and told the residents to evacuate. They did, police said — and thanks to that, they were unharmed.

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Firefighters from the Lynbrook Fire Department then battled subfreezing temperatures to put out the blaze.

Photos from the scene show the second floor in flames. Photos after the fire show the roof collapsed.

There were no reported injuries.

News 12 Long Island is reporting that the passer-by was a member of the Hewlett Fire Department, but police said that could not immediately be confirmed. Calls to fire officials were not immediately returned on Monday.