The operation, which started on Thursday, involves aircraft and several teams of rescuers. No signs of the missing helicopter have been spotted so far and the fate of the three people on board is unknown, the official said.
"The search operation involved 125 rescuers, two helicopters and two planes on Saturday, but had to be interrupted before the nightfall," the source said.
"We resumed the rescue effort on Sunday when the visibility improved," he said.
The local emergencies ministry department said Thursday that the missing Mi-2 helicopter was flown by an experienced test pilot carrying the president and vice president of the small aircraft association Flag on board.
The helicopter was last seen Tuesday evening. Officials said it may have made an emergency landing in bad weather. Local witnesses confirmed seeing a Mi-2 flying at a low altitude just above tree tops Tuesday.
The Mi-2 is an eight-passenger utility helicopter with a flight range of about 600 kilometers (370 miles).
