TEHRAN -- Southeast Iran was hit by the most powerful earthquake to strike the country in 40 years on Tuesday, and its reverberations were felt as far away as India, but Iranian officials said the tremor had originated so deep underground, and in such a sparsely populated area, that it caused relatively few casualties and only minor damage.
The authorities in Iran had initially feared hundreds of deaths from the 7.8-magnitude earthquake, but scaled back their assessment as it became clear that its depth, initially reported to be only about 10 miles beneath the surface, was more than 56 miles beneath. The shallower the quake, the greater the ground motion and potential for damage.
The earthquake, which struck at 3:14 p.m. local time, was felt in several countries in Asia, rocking buildings in the Indian capital, New Delhi, sending panicked residents of Karachi, Pakistan, fleeing into the streets and causing tremors through Persian Gulf states.
The United States Geological Survey said the earthquake's epicenter was near Khash, Iran, not far from the border with Pakistan, in the Iranian province of Sistan and Baluchistan.
The province, with vast expanses of unpopulated territory, is home to nearly two million people. Most are concentrated in Zahedan, the provincial capital, and the cities of Saravan and Khash.
The semiofficial Fars news agency quoted Iran's seismology center as saying the earthquake was the worst in 40 years.
But Mohammad Sarvar, head of Iran's Emergency Medical Service, was quoted by the news agency as saying the power of the earthquake overstated its effects.
"We still do not have an accurate number of casualties but due to the low population density, we foresee the number of casualties is not high," he was quoted as telling Fars, adding that officials the city of Saravan were not reporting any casualties. Still, other officials said a precautionary state of emergency was declared there.
In Zahedan, Mahmoud Taheri, general manager of crisis infrastructure and telecommunication affairs, said in an interview by telephone that he had felt the earthquake but that it had not caused any damage. He also said there were no reports of casualties or serious damage in Saravan, which was the closest city to the earthquake's epicenter.
Mr. Taheri said two villages, Mak Soukhte and Lolokdan, about 35 miles from the epicenter, had been damaged, but that "fortunately there are not many people living in these areas."
Iran is vulnerable to earthquakes, some of which have taken tens of thousands of lives. In 2003, a 6.6-magnitude earthquake near the city of Bam killed at least 26,000 people, and in 1990 at least 30,000 people died in an earthquake along the Caspian Sea. Last week, a 6.1-magnitude earthquake hit in Bushehr Province, home to Iran's main nuclear reactor, killing more than 30 people.
Sistan-Baluchistan Province is among the poorest of Iran. Most residents are Sunni Muslims, a minority in the largely Shiite Muslim country, and many are from the Baluchi tribe, which originates in Iran and Pakistan. The area is known for its drug trade and is regularly the scene of bombings carried out by separatist groups.
In Karachi, the southern port city in Pakistan, local television broadcast images of people standing in the streets after fleeing high-rise buildings. Tremors were felt most strongly in southern and central parts of Pakistan.
"It seems as if the buildings will fall any minute," an unidentified man in Karachi told GEO News, a private television news network.
The only report of fatalities, however, came from the adjoining province of Baluchistan, which borders Iran, where the Human Rights Commission of Pakistan reported five deaths. Tahir Hussain, a lawyer with the human rights group, said the victims were all in the remote town of Panjgur, 50 miles from the border.
"A wall collapsed and five people lost their lives, including three children and a woman," he said, speaking by phone from Quetta, the capital of Baluchistan.
In New Delhi, which is periodically shaken by temblors, buildings shook for more than 10 seconds and, in some areas, frightened people ran into the streets. No injuries were reported, nor were there any early reports of property damage there.
Jim Yardley contributed reporting from New Delhi, Salman Masood from Islamabad, Pakistan, and Gerry Mullany from Hong Kong.
This article originally appeared in The New York Times.