Despite unilateral cease fire declared by the Chinese after the 1962 war, tensions still remained high all along the Sikkim-Tibet border. In September 1967 the 70 field coy Engineers was deployed to lay a wire fence along the distributed border area of Nathu La to end the frequent skirmishes between Indian and Chinese forces. The 18 RAjput Regiment led by Brigadier Harbhajan Singh to provide protection to the Engineers also took up their positions.

No Sooner had the work commenced then the Chinese opened fire on the Indians from the front and from the flanks. The Major led the charge at the attackers. He bayoneted three Chinese soldiers and then he turned attention to a light machine gun, the enemy was using. Even as he hurled a grenade at the gunner, bullets ripped through his body killing him instantly.

Major Harbhajan Singh was honoured with the Mahavir Chakra posthumously.