The fire gutted the church at Broderick and California streets. No injuries were reported, and firefighters prevented the flames from spreading beyond the church, according to church officials and the San Francisco Fire Department.
New drone video released by the fire department shows the intensity of the blaze, which burned for several hours despite crews arriving within three minutes of the initial call. About 100 firefighters responded to battle the fire.
"I'm heartbroken," said Senior Pastor Mark Ferrell.
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"This church means a lot to me and my family," Ferrell said. "And it's like losing a friend."
Ferrell said the church has deep personal significance for his family.
"I've been here for 20 years. I had the opportunity of being married here 20 years ago. As well as my father was baptized here when he was 12 years old," said Ferrell.
Church officials said construction crews were working on the building when the fire began on an upper level near the windows before spreading to the roof.
"Over past few years, need to do some resurfacing of sandstone, we've had to reseal it. That was what was going on at this time," Ferrell said.
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"Unfortunately a building like this on the inside has a lot of dried timber. Just a spark can get going very quickly," he added.
Lt. Mariano Elias of the San Francisco Fire Department said investigators determined the fire originated during construction work.
"The construction workers were the cause of the initial fire and it spread through the building," Elias said.
The church, originally built in 1892 by shipbuilders, suffered extensive damage. On Wednesday, investigators continued examining the scene and sifting through debris.
Fire officials said drone technology equipped with thermal imaging helped incident commanders identify hot spots during the firefighting effort.
"To show him the thermal points of heat registered on the screen to allow him to direct crews on where to focus their efforts," Elias said.
Despite the loss, church leaders said the congregation intends to rebuild.
"This is a very sad situation, a very tragic situation," said Ricardo Viloria, president of the Central California Conference of Seventh-day Adventist Church.
"This church from come back from the ashes," Viloria said.
Community members also expressed gratitude that firefighters and police officers were able to protect nearby homes and keep the blaze from spreading.
"We are thankful for what the fire department did. What the police department did," Ferrell said.
Church officials said the congregation will temporarily move services to another Seventh-day Adventist church located two blocks away while leaders determine the next steps in the rebuilding process.