India is violating an 1890 border agreement between Britain and China that previous Indian governments pledged to uphold, Beijing has said, adding that the treaty must be respected to end what it sees as a "very serious" incursion by India.

Key points: The border dispute near Bhutan has been going on for a month now

The border dispute near Bhutan has been going on for a month now China's Foreign Ministry says the incursion by India is in violation of international law

China's Foreign Ministry says the incursion by India is in violation of international law Experts believe the stand-off is part of a bigger China-India power struggle

The border stand-off on a plateau next to the mountainous Indian state of Sikkim, which borders China, has ratcheted up tension between the neighbouring giants, who share a 3,500-kilometre frontier, large parts of which are disputed.

According to the Chinese interpretation of events, Indian guards crossed into China's Donglang region early in June and obstructed work on a road on the plateau.

Troops from the two sides then confronted each other close to a strategic valley controlled by China that separates India from Bhutan — a close Indian ally — and gives China access to the so-called Chicken's Neck, a thin strip of land that connects India to its remote north-eastern regions.

Sorry, this video has expired China accuses India of violating 1890 border agreement ( Beverley O'Connor )

Chinese Foreign Ministry spokesman Geng Shuang told a daily news briefing that the Sikkim part of the border had been settled in the 1890 agreement, and previous Indian governments had many times affirmed that in writing.

"Pacts must be respected — this is a basic principle of international law," Mr Geng said.

Mr Geng added that the Indian troops crossing onto the Chinese side were in violation of this historical agreement and a United Nations charter.

"The nature of this is very serious," Mr Geng said, reiterating a demand for India to withdraw its troops to its side.

India's Ministry of External Affairs referred to a statement it made last week, when it warned China that construction of the road near their common border would have serious security implications.

'China and India's rivalry for power and influence'

Despite the tensions, Chinese President Xi Jinping and Indian Prime Minister Narendra Modi have maintained economic relationships. ( Reuters: Damir Sagolj, file )

Analysts in New Delhi said that India had intervened on behalf of Bhutan — as the tiny Himalayan Kingdom was not party to the 1890 agreement between Britain and China, the dispute was between China and Bhutan over where their common border lies.

Bhutan said last week that the road was being built inside its territory.

However, some experts believe more is at stake than the territories in question.

"The broader political context is that it's not about Bhutan, it's not about that territory — it's about China and India's rivalry for power and influence," regional expert Dr Mohan Malik told the ABC.

"Given the growing power asymmetry between China and India, China wants to lock in geopolitical and geo-economic advantages."

Chinese President Xi Jinping and Indian Prime Minister Narendra Modi are attending a summit of the G20 group of nations in the German city of Hamburg later this week.

Mr Geng would not be drawn on whether the two could meet there, saying bilateral meetings for Mr Xi at the summit were being arranged.

ABC/wires