At least 20 Indian soldiers, including a senior officer, have been killed in a confrontation with Chinese troops along a disputed border high in the Himalayas, the Indian army said on Tuesday.
Thousands of troops on both sides have been facing off in the area for more than a month.
Beijing blamed India for the clash on Monday and the editor of the government-affiliated Global Times said the Chinese military had also suffered casualties.
China's military demanded that India immediately stop all infringements and provocative action against its troops, and return to talks to resolve their disagreements.
The remarks by Zhang Shuli, spokesman for the Chinese Western Theatre Command, were published by Chinese state media and the military's official newspaper.
The Indian army said a “violent face-off” took place in Galwan valley in the Ladakh region on Monday night.
“The loss of lives on the Indian side includes an officer and two soldiers,” it said.
“Senior military officials of the two sides are currently meeting at the venue to defuse the situation.”
The Chinese Foreign Ministry called on India not to take any action or stir up trouble.
"What's shocking is that on June 15, the Indian side severely violated our consensus and twice crossed the border line and provoked and attacked the Chinese forces, causing a violent physical confrontation between the two border forces," ministry spokesman Zhao Lijian told Reuters in Beijing.
"China is raising strong opposition and stern representations to the Indian side on this."
India and China fought a brief border war in 1962 and have not been unable to settle their border dispute despite talks spread over two decades.
The incident is the first confrontation between the two Asian powers in which soldiers have died since 1975.
Soldiers from the two countries, backed by armoured vehicles and artillery, have been facing off just a few hundred metres apart for more than a month in the Ladakh region near Tibet.
Army officers and diplomats have held meetings to try to end the impasse, with no breakthrough.
Indian officials say Chinese soldiers crossed the boundary in Ladakh in early May at three different points, setting up tents and guard posts and ignoring verbal warnings to leave.
The Asian giants have rival claims to vast areas of territory along their mountainous 3,500-kilometre border, but the disputes have remained largely peaceful since the 1962 war.
Indian military officials said previously Chinese soldiers had entered into India's side of the de facto border at several locations in early May.