BEIJING: China and India accused each other of firing shots first across a flashpoint Himalayan border, intensifying a months-long standoff between the nuclear-armed neighbours that has already claimed at least 20 lives.

China said Tuesday its soldiers took "countermeasures" after Indian soldiers opened fire in a contested mountainous region in Ladakh. India was guilty of a "severe military provocation" on Monday after its soldiers crossed the Line of Actual Control in the western border region of Ladakh and "opened fire", according to China's Defence Ministry.

New Delhi was swift to give its own account, accusing Chinese border forces of "blatantly violating agreements" and firing "a few rounds in the air" to intimidate their Indian rivals. "Despite the grave provocation, (our) own troops exercised great restraint and behaved in a mature and responsible manner," the Indian army said in a statement.

Indian media reported late Tuesday, citing government sources, that the Chinese troops had rods, spears and clubs, and published a photo appearing to show soldiers holding staffs topped with blades. It is first confirmed shooting across the contested frontier for decades, where skittish border forces by convention do not use guns to avoid escalations of violence in remote terrain.