Twenty Indian soldiers were killed in a "violent face-off" with Chinese troops at Galwan Valley in Ladakh on Monday night, the Indian Army has said in a statement.
Forty-three Chinese soldiers were also killed or seriously injured during the clash, reports NDTV citing an ANI report based on unnamed sources.
This is the most serious escalation at the border in five decades, at a time when soldiers of both sides were in the process of disengagement.
An Indian army statement on Tuesday morning confirmed the death of a colonel and two jawans and spoke of "casualties on both sides". In another statement last evening, the army added that 17 more critically injured were "exposed to sub-zero temperatures... (and) succumbed to their injuries".
The army statement opened by saying Indian and Chinese troops "have disengaged" at the Galwan area where they earlier clashed on the night of June 15/16.
Agence France Presse quoted an Indian army source as saying the incident involved no shooting but "violent hand-to-hand scuffles". The soldiers threw punches and stones at each other and the Chinese troops allegedly used rods and nail-studded clubs during the fight that lasted for hours until midnight on Monday, according to reports.
China's defence ministry confirmed the incident had resulted in casualties but did not give details.
India blamed the clashes on "an attempt by the Chinese side to unilaterally change the status quo there", rebutting China's claims that Indian soldiers crossed the border.
"India is very clear that all its activities are always within the Indian side of the Line of Actual Control. We expect the same of the Chinese side," said foreign ministry spokesperson Anurag Shrivastava.