Dozens of firefighters were still on the scene early Monday of an enormous four-alarm fire that engulfed a 19th-century Serbian Orthodox cathedral in Flatiron on Sunday night, drawing nearly 170 firefighters at its peak. A spokesperson for the FDNY confirmed that the blaze was under control by 10:30 p.m.; firefighters on the scene this morning continued to hose down stubborn pockets of fire.

"We were not immediately able to determine the cause so it's being deemed suspicious, and is under investigation," FDNY Deputy Assistant Chief Michael Gala told reporters on Monday. He added that the flames were so intense that the firefighters were able to gain entry to the cathedral only briefly.

"We were only committed inside the structure for a few minutes before we were overwhelmed," he said.

[UPDATE 12:00 p.m.]: The FDNY confirmed on Monday that the ‘suspicious’ label is applied to all fires without a known cause. Spokesman Frank Dwyer added in a statement that nefarious behavior was not suspected at this time. "To clarify, the fire is under investigation by FDNY Fire Marshals. It is not believed to be, nor has it been labeled as, suspicious," he said.

The Department of Buildings has already conducted a preliminary inspection of the site, and confirmed on Monday that the building is structurally sound. "There is no immediate danger of collapse," a spokesperson stated. "DOB continues to inspect the structure for areas of loose debris in danger of falling." In the meantime, Local City Council member Corey Johnson has called for a "full investigation" into the cause of the fire.

"Determining the fire's cause is vital," he said in a statement. "This is a huge loss for the community. In addition to being a place of worship, this historic building was a New York City landmark, treasured by the people of Flatiron and Chelsea."

The fire broke out around 6:50 p.m. on Sunday at the Serbian Orthodox Cathedral of St. Sava, on West 25th Street between Fifth and Sixth avenues. The congregation of about 700 parishioners had gathered earlier that day for the 10:00 a.m. Orthodox Easter mass. The Post reports that many stayed after the service for a luncheon, but the church was empty when the fire broke out. According to the FDNY, there were no significant injuries; one person was treated for smoke inhalation.

"It's amazing those timbers didn't burn all the way," said a person associated with the church, on the scene Monday morning. While the structure of the church is stone with steel girders, the now-skeletal roof is made of wood—a gothic timber hammer-beam design popularized in England. The church associate, who spoke on the condition of anonymity, noted that the structure still looked majestic this morning, despite the gutted roof.

He added that the church is insured, but expressed concern about whether the insurance company is solvent enough to cover the damage. "It could be a tragedy with a benefit, if people rally to save it," he said, adding that the church is located on an extremely valuable parcel of land.

Luxury real estate developer Madison Equities filed suit against St. Sava in December 2014, accusing the church of failing to keep the terms of a letter of intent that both parties signed in May of that year. The Real Deal reported at the time that Madison had agreed to pay for improvements to the sanctuary in exchange for nearly 200,000 square feet of air rights above the church and its adjacent property.

The suit, which was dismissed last December, alleged that the church hired a commercial broker, Tenantwise, to negotiate on its behalf—a detail they failed to disclose to Madison Equities before the letter of intent was signed. The church then allegedly asked Madison to pay a $13.5 million brokers fee, which Madison argued was excessive. The church associate on the scene of the blaze Monday said that the developers were still interested in the church's air rights.

Built in 1855, the gothic cathedral at 13 West 25th Street was consecrated as Trinity Chapel, an Episcopal Church. It transferred to the Serbian Orthodox Church in the 1940s. The NY Times reports that it was added to the National Register of Historic Places in 1968, the same year it was granted historical landmark status. A lot adjacent to the church hosts the Chelsea Flea Market.

Madison Equities did not immediately respond to a request for comment. A person who answered the number associated with St. Sava declined to give his name. He said, "At this time we don't know anything, and we don't talk to anyone yet."

Additional reporting by Jen Chung.