Two Chinese patrols came on foot, two more arrived in military vehicles, and a Chinese helicopter flew overhead. With all the activity, the Indian authorities failed to notice until the next morning that about 30 Chinese soldiers had pitched three tents in an area both countries claim.
Indian military officials protested. The Chinese stayed put. India protested again. The Chinese, who had with them a few high-altitude guard dogs, responded by erecting two more tents and raising a sign saying, in English, "You are in Chinese side."
As the dispute enters its third week, alarm in the Indian capital is growing. At a Thursday news briefing, Syed Akbaruddin, the spokesman for India's Ministry of External Affairs, said, "There is no doubt that in the entire country this is a matter of concern."
But the prime minister has sought to play down the dispute.
"It is a localized problem," Prime Minister Manmohan Singh said Saturday. "We do believe it can be solved. We have a plan. We do not want to accentuate the situation."
Still, jingoistic comments are growing by politicians linked to both the opposition and the government.
"This government is cowardly, incompetent and good for nothing," said Mulayam Singh Yadav, an important regional leader allied with the ruling coalition.
Arun Jaitley, a leading opposition politician, said in Parliament on Thursday, "You may have some security options, you may have some diplomatic options, but being clueless is not an option."
In China, a Foreign Ministry spokeswoman denied that Chinese troops had crossed into Indian territory and said the dispute would be resolved peacefully and through appropriate channels.
"I would also like to point out that China and India are neighbors and their borders haven't been demarcated," said the spokeswoman, Hua Chunying, at a news conference last week in Beijing. "As such, it is difficult to avoid this or that kind of problem."
On Thursday, the online edition of People's Daily ran an editorial that urged China to continue friendly relations with India, but said China should not "indulge" India's "bad habits" and in particular the "lies" of the Indian media.
Although Indian and Chinese politicians have not described the reasons for the dispute, Indian press reports have stated that Chinese officials have demanded the Indian authorities demolish some newly constructed bunkers and reduce patrols in the area.
As its economic might has grown, China has become increasingly assertive in its territorial claims across Asia. In disputes with Japan, Vietnam and the Philippines, among others, China's claims revolve around islands or sea lanes that are potentially rich in oil and gas deposits. What puzzles Indian analysts is that China has chosen to squabble over a barren moonscape frequented only by nomadic cattle herders.
"It's an inexplicable provocation," said Gen. Vasantha R. Raghavan, a former top Indian military commander who once commanded the region in dispute. "There is something happening inside China which is making the military act in an irrational manner."
Trade between China and India is growing rapidly. Foreign Minister Salman Khurshid of India is expected to visit Beijing next week, and Prime Minister Li Keqiang of China is scheduled to visit India three weeks later on his first official trip abroad since taking office in March. Indian and Chinese officials have stressed that relations remain friendly, and Indian officials say that Khurshid still intends to go to Beijing. But there are growing calls in India for both trips to be canceled.
Raghavan said the dispute was likely to accelerate improving military ties between India and the United States - a development that is not likely to be welcomed by China.
M. Taylor Fravel, a professor of political science at the Massachusetts Institute of Technology and an expert on China's border issues, said that China might be responding to local concerns about Indian military construction in the disputed area. But he said information about the incursion was sketchy.
The dispute is playing out hundreds of miles from what has long been seen as the most contested area between the countries - a stretch of land that separates Tibet, occupied for decades by China, and the Indian state of Arunachal Pradesh. Chinese soldiers crossed that part of the border during the 1962 war and took over a section of Arunachal Pradesh, including the culturally Tibetan area known as Tawang, before decamping and returning to China. In 2009, China became more vocal in its claims to parts of Arunachal Pradesh.
The latest spat between India and China is bound to resolve itself this year, one way or another. In six months, snow and bitterly cold weather will make the Chinese encampment very difficult, if not impossible, to maintain.