Update, 6:30 p.m.:
Anchorage police said the situation was resolved peacefully on Thursday evening, and that the man had surrendered to officers.
"Negotiators were able to work with the distraught citizen and get him to walk back towards his vehicle which was parked on Campbell Airstrip Road," spokeswoman Jennifer Casto said in an email.
Castro said police were speaking to the man.
Anchorage Police are asking people to avoid the trails near Campbell Airstrip Road, where they said a distraught man with a gun was threatening to kill himself Thursday afternoon.
The man had left his family and driven to Campbell Airstrip Road, then headed into the woods on the North Bivouac trail, said police spokeswoman Jennifer Castro.
Police have blocked access to the road, Castro said, and more than 20 police officers were looking for the man. They were also clearing people off trails in Far North Bicentennial Park, and near Service High School and the Hilltop Ski Area, Castro added.
"We don't know where he's going to come out," she said.
The man has a cell phone and had been in touch with his family, Castro said, but "he's not answering when we're calling him."
Reach Nathaniel Herz at firstname.lastname@example.org or 257-4311.