The plane went down shortly after 6:30 p.m. local time, about four miles from its destination. It had taken off from Bethel, Alaska, about 400 miles west of Anchorage.
"We have found a crash site and are working on identifying what needs to be done with the passengers that are there," said Megan Peters, a spokeswoman for the Alaska state troopers. "There are survivors and we are working our best to get them help."
The dead were identified as pilot Terry Hansen and three passengers: Rose Polty, Richard Polty and the infant, Wyatt Coffee.
There was no immediate word on the condition of the six survivors, but an airline spokeswoman said they were injured.
They were identified as Melanie Coffee, Pauline Johnson, Kylan Johnson, Tonya Lawrence, Garrett Moses and Shannon Lawrence.
Troopers and an air ambulance responded to the scene after an emergency locator beacon signal helped pinpoint the crash site.
The cause of the crash was not immediately known, but two investigators from the National Transportation Safety Board were being sent to the scene Saturday.