Authorities were investigating the cause of an explosion that damaged a Van Nuys apartment building Saturday night.

The Los Angeles Fire Department was alerted at 5:38 p.m. to the blast in the 7300 block of Woodman Avenue, according to Connor Thompson, an LAFD spokesman.

The damage was confined to a single apartment unit whose occupants — two adults and one child — were not home when the explosion occurred, Thompson said.

No one was injured in the blast, which blew out the apartment’s windows, Thompson said. The Red Cross was helping the occupants find new housing Saturday night, he added.

Maronzio Vance, who lives across the street, was inside his apartment when he heard a massive explosion. “When I got the courage to go outside,” he told The Times, “I see the wall is gone. The wall of the apartment is gone. It’s like something you’d see in a Marvel movie.”

Vance filmed a video of the building showing shattered glass and blown-out window screens strewn across the sidewalk. He said he believed it was a gas explosion. “You can smell the gas a mile away,” he said.

City officials had recently knocked on doors at Vance’s apartment building, which he said is managed by the same company that oversees the one where the blast occurred, and talked of shutting off the gas because the owner or property manager had failed to pay the bill, Vance said.

Forty-six firefighters responded to the explosion, whose cause is being investigated, Thompson said. Inspectors from the city’s Department of Building and Safety will conduct an “extensive damage report” as well, he said.