Modi visited the mountainous Arunachal Pradesh state aimed at garnering support for his Hindu nationalist Bharatiya Janata Party ahead of Indian elections due by May, Presstv Reported.
"The Chinese government has never recognized the so-called Arunachal Pradesh, and is firmly opposed to the Indian leader's visit," Chinese Foreign Ministry spokesperson Hua Chunying said Saturday.
She urged the Indian leadership to refrain from any action that may "complicate the boundary question" which has remained a sensitive issue despite recent efforts to improve bilateral ties.
China claims Arunachal Pradesh as southern Tibet, a remote, high-altitude stretch of the Himalayan border that stoked fears of another war following a 73-day face-off in 2017.
"China urges the Indian side to ... respect China's interests and concerns, cherish the momentum of improving relations between the two countries, and refrain from any actions that intensify disputes and complicate the border issue," Hua said.
India shot back, saying Arunachal Pradesh was "an integral and inalienable part of India."
"Indian leaders visit Arunachal Pradesh from time to time, as they visit other parts of India. This consistent position has been conveyed to the Chinese side on several occasions," India's Foreign Ministry said.
In 1962, the two Asian giants fought a brief, yet bloody, war over Arunachal Pradesh, with Chinese troops temporarily capturing part of the territory.
In 2017, they were again engaged in a standoff in Bhutan's Doklam region after the Indian army sent troops to stop the construction of a military road by China.
After a two-month standoff, troops from both sides withdrew and the countries sought to rebuild trust. The 3,500 km border between the nuclear-armed neighbors has been calm ever since.
Modi and Chinese President Xi Jinping met a number of times last year to give impetus to trade discussions but progress has been very slow.
As well as disputes over their border, the two countries are vying for influence in the Indian Ocean and squabbling over President Xi’s signature Belt and Road infrastructure initiative.
Indian officials, however, say China has been more flexible than before with regard to opening up its markets to Indian pharmaceutical products and IT services.
Last year, bilateral trade reached $89.6 billion, with a deficit of $62.9 billion in China’s favor.