(CNN) -- State and federal authorities are investigating the apparent double homicide of two Coast Guard members who were shot dead on an island off Alaska's coast, prompting the lockdown of their base and at least one nearby school.
It's possible that the shooter, or shooters, remain at large, according to a Coast Guard statement.
"We're treating this as a double homicide," said FBI spokesman Eric Gonzalez, who noted that the slayings occurred inside the Coast Guard Communications Station Kodiak.
Coast Guard investigators, island police, state troopers and the FBI are investigating the incident.
"We are deeply saddened that we lost two shipmates," Capt. Jesse Moore said in a news release. "This is a rare occurrence, and we are going to do everything possible to ensure we find out exactly what happened."
The victims have not yet been identified by name.
Their base is on what the city of Kodiak's website calls the second-largest island in the United States, situated in the Gulf of Alaska about 250 miles southwest of Anchorage. The borough of Kodiak Island has about 13,600 people, according to the U.S. Census Bureau.
The Coast Guard facility normally houses about 60 people.
"It's definitely the topic of conversation right now," said Cheryl Montgomery, a manager at Henry's Great Alaskan Restaurant. "The town's people are very much on edge here."
Montgomery said that her restaurant remained abuzz Friday with rumors of who may have carried out the shootings, though "nobody knows what's actually going on."
"There's so many weird and bizarre stories running around right now," she said.
City Manager Aimee Kniaziowski said her office has not been instructed to take additional security precautions.
"We're just conducting our business until we're told otherwise," she said.
The small town is reeling from the loss, she added, calling the killings "devastating."
Peterson Elementary School, which is on Coast Guard property in Kodiak, went into lockdown mode around 8:30 a.m. (12:30 p.m. ET) after school leaders got a call from military police, Principal Beth Cole said.
By 11 a.m., they shifted to "lock in" mode, allowing for more movement within the school, though lunch was still delivered to students in class as a precaution, Cole said. No people were allowed in and out of the building all day.
Three other elementaries, one middle school and one high school on the island were also affected, school district Superintendent Stewart McDonald said.
Those schools were on "lock in" status starting at 11:30 a.m. so that activities could continue as normal, except for the fact that no one could enter or leave the buildings. At the time, Kodiak High School was hosting an Alaska Association of Student Government meeting involving youths from around the state.
All restrictions for the district's roughly 2,200 students were called off about 1 p.m. after state troopers called school officials and said that operations could return to normal, according to McDonald.
CNN's Alta Spells contributed to this report.