A helicopter carrying Arunachal Pradesh chief minister Dorjee Khandu and four others, including two crew members, from Tawang went missing immediately after take-off on Saturday morning.
Khandu, accompanied by two of his personal aides, had taken off from Tawang at 9:56am and was to land at Itanagar at 11:30am.
It was last sighted at Sela Pass, 20 minutes after taking off from Tawang, defence sources in Shillong said.
DIG Robin Hibu said the helicopter went missing after take-off.
The air force has pressed into service two helicopters in search operations to locate the missing chopper.
56-year-old Khandu, who had served in the intelligence wing of the Indian Army, was sworn on April 9, 2007 as the fifth chief minister of the state, replacing Gegong Apang.
This is the third helicopter to get into trouble in the Northeast in the last fortnight.
In the April 19 incident, a Pawan Hans helicopter crashed in the mountains of Tawang, bordering Tibet, killing all 17 people on board.
The helicopter crashed not far away from the helipad and the DGCA had found that proper fire-fighting facilities could have saved lives.
In the other incident, an army helicopter crashed near Gangtok killing four occupants on board.
The helicopter was flying from Guwahati to Itanagar via Tawang, Pawan Hans sources said.