The fighter jet crashed at 1:15 PM with the pilot, Flight Lieutenant Yogesh Yadav, suffering critical injuries and the wreckage catching fire, Colonel Gurung of 27 Mountain Division stationed in North Sikkim told reporters.
According to eyewitnesses, there was a loud bang before the pilot bailed out.
Local people reached the crash site and rescued the pilot who was conscious and taken to a school at Lik, Col Gurung said.
The Army and Airforce were trying to land a helicopter in the schools grounds to evacuate the pilot to Siliguri, he said.
If the helicopter is unable to land, the pilot would have to be carried from Lik to the North Sikkim Highway from where he would be taken by road, he said.
The fire, which broke out in the wreckage of the aircraft, was under control, Col Gurung said.
The aircraft had taken off from Bagdogra airport near Siliguri in West Bengal, he said.