(Updated: Six family members still missing in Annapolis mansion fire)

A waterfront mansion in Annapolis was destroyed in a four-alarm fire Monday morning, and officials said the ­cybersecurity executive who lived there, his wife and four other relatives were unaccounted for that night.

Capt. Russ Davies, a spokesman for the Anne Arundel County Fire Department, said firefighters spent most of Monday extinguishing hot spots in the 16,000-square-foot home and could not search it because much of the structure had collapsed into the basement.

“It will take considerable work to move steel beams and stabilize the area,” Davies said, adding that “thousands of gallons of water will have to be pumped out of the basement.” He said federal rescue teams with special lifting equipment were expected Tuesday.

Firefighters responded to a 3:30 a.m. alarm at a house on Childs Point Road, near where Church Creek empties into the South River. Property records indicate that Donald and Sandra Pyle bought the property in 2005. It sits on eight acres and was assessed at more than $6.6 million. So far, Davies said, “we have not seen anything to make us believe this is a suspicious fire.”

Firefighters work to put out a fire Monday at a home on Childs Point Road, in Annapolis, Md. (Tim Pratt/AP)

Although the other missing relatives were initially described as the couple’s children, the Capital Gazette of Annapolis, citing a letter from their school, identified them as Donald and Sandy Pyle’s grandchildren.

Donald Pyle is chief operating officer of ScienceLogic, a Reston-based cybersecurity company that monitors networks for private and government ­clients, including the Pentagon. The company last year announced a partnership with L-3 Data ­Tactics of McLean to bring “big data” monitoring to the U.S. intelligence community and federal government.

Pyle previously helped launch Juniper Networks of Herndon, Va., and was chief executive of Laurel Networks of Pittsburgh and Netcordia of Annapolis.

In an interview with The Washington Post in October, he said he grew up in northern Baltimore County and worked in a family business as a teenager. He switched to information technology after college, he said, because “I was looking for an industry that was in its infancy and something that would have growth potential.”

Davies said officials were told Monday that the Pyle family was preparing to go on a trip and might be out of town. But investigators were not able to reach them by cellphone and have spoken with relatives who could not reach them either.

“It’s a possibility we have to consider,” Davies said, when asked whether the family might have been trapped inside the burning house. “Our intent is to do that search and look for them.”