Defence sources said 30 columns of the Indian Army comprising 2,400 personnel from Tawang and Tenga were pressed in different locations along the Indo-Bhutan border on ground search. Six ITBP teams with 25 personnel each have also joined the ground search operations.
More Army columns are likely to join soon while two Chetak helicopters from Guwahati and an MI-17 IAF chopper from Tawang are on sorties.
IAF officials said in New Delhi that two Sukhoi-30 warplanes have been dispatched from Bareli to scan the general area using their special radars.
Sukhoi planes have helped in locating the wreckage of the missing chopper of the then Andhra Pradesh Chief Minister Y S Rajasekhara Reddy in September, 2009. Reddy and four others on board the chopper died.
Though the choppers were scheduled to begin search operations at 5.30 am, inclement weather delayed them by more than three hours.
Search teams from the neighbouring Bhutan have also launched rescue operation in seven districts of the country, sources said.
Union Ministers Mukul Wasnik and V Narayanswamy are on their way to Itanagar from New Delhi to monitor the search operations, official sources said.
The four-seater single-engine Pawan Hans helicopter AS-B350-B-3 chopper went missing yesterday after 20 minutes of its take off from Tawang at 9.56 am last morning with five on board including crew members Captain J S Babbar, Captain T S Mamik, Khandu`s security officer Yeshi Choddak and a lady Yeshi Lhamu, sister of Tawang MLA Tsewang Dhondup.
The chopper was to land at Itanagar at about 11.30 am.
The Guwahati air traffic control had reportedly received the last radio communication from the chopper near Sela Pass area, 20 minutes after take off from Tawang.
Sela Pass is at about 13,750 feet above sea level where weather changes drastically within minutes.
Indian Ambassador to Bhutan Pavan Verma said that the operations were being done by the Indian Government and the Bhutanese authorities were providing all cooperation.
"Since yesterday the Bhutanese have been most cooperative," he said.
Khandu`s helicopter was the third to get into trouble in the northeast in the last fortnight.
On April 19, a Pawan Hans helicopter crashed at Tawang heliport, bordering Tibet, killing 17 people and injuring six others on board.
Arunachal has witnessed a large number of air crashes.
In November 1997, the then Minister of State for Defence N V N Somu, Major General Ramesh Nagpal and two others died when their Cheetah helicopter hit a 1,300 feet peak, 40 kilometers from Tawang.
In May 2001, Arunachal Pradesh Education Minister Dera Natung and five others were killed when their Pawan Hans aircraft crashed near Tawang because of poor visibility.
In 2009, an IAF AN-32 aircraft crashed at Mechunka killing all 13 defence personnel on board. Eleven Air Force personnel and an Army Lieutenant Colonel were killed when an Air Force MI-17 helicopter crashed near the China frontier on November 19, last year a minute after take off.