Updated

A plane believed to be carrying eight people, including former Sen. Ted Stevens and former NASA Administrator Sean O'Keefe, crashed in southwest Alaska and rescue crews were trying to reach the wreckage Tuesday morning, authorities said.

Alaska National Guard spokesman Maj. Guy Hayes said there were possible fatalities. Five people were on scene early Tuesday helping the crash victims, he said. It was unclear how they reached the site.

A U.S. government official told The Associated Press that Alaska authorities have been told that Stevens, a former longtime Republican senator, is among several passengers on the plane. The official, who spoke on grounds of anonymity, says Stevens' condition is unknown.

The federal official declined to be publicly identified because the crash response and investigation are under way.

Defense contractor EADS North America said Tuesday morning that O'Keefe, the current CEO of the U.S.-based division of the European company, was a passenger on the small plane. The company said it has no further information about O'Keefe's status.

Hayes said the Guard was called to the area about 20 miles north of Dillingham at about 7 p.m. Monday after a passing aircraft saw the downed plane. But severe weather has hampered search and rescue efforts.

Hayes said he was told by Alaska State Troopers that there were "eight or nine" people on board, though a spokeswoman for the troopers, Megan Peters, refused to comment.

She said all the agency could say for sure is that a plane went down and crews were "aggressively" trying to reach the crash site but having difficulty doing so. As of 4 a.m. Tuesday, she said she still hadn't received word that crews had reached the site.

"I can't go beyond, 'We're responding to a plane crash,"' she said.

The National Weather Service reported rain and fog at Dillingham, with low clouds and limited visibility early Tuesday.

Conditions ranged from visibility of about 10 miles reported at Dillingham shortly before 7 p.m. Monday to 3 miles, with rain and fog, reported about an hour later, according to the agency.

Stevens, a moderate Republican, was appointed to the Senate in 1968 and served longer than any other Republican in history. He directed billions of dollars to Alaska over the years.

But one of his projects -- infamously known as the "Bridge to Nowhere" -- became a symbol of pork-barrel spending in Congress and a target of taxpayer groups who challenged a $450 million appropriation for bridge construction in Ketchikan.

Stevens' standing in Alaska was toppled by corruption allegations and a federal trial in 2008. He was convicted of all seven counts -- and narrowly lost his Senate seat to Democrat Mark Begich in the election the following week.

But five months after the election, Attorney General Eric Holder sought to dismiss the indictment against Stevens and not proceed with a new trial because of prosecutorial misconduct by federal prosecutors.

A National Transportation Safety Board investigative team has been dispatched from Washington, D.C., to the crash site and was expected on the ground Tuesday morning.

In Washington, a Federal Aviation Administration spokesman said the aircraft is a DeHavilland DH3T registered to Anchorage-based GCI Communication Corp.

Dillingham is located in northern Bristol Bay, about 325 miles southwest of Anchorage.