ISLAMABAD, Pakistan — A Pakistani passenger plane crashed in fog and intense rain in the Himalayan foothills near this capital city on Wednesday morning, killing all 152 people on board in the country’s deadliest domestic plane crash, according to civil aviation and airline officials.

Rescue helicopters fought against thick smoke and flames as they tried to find survivors amid the wreckage — at least an hour’s drive into the high ground above Islamabad — but hours after the crash, Pakistani officials said that none of the 146 passengers or 6 crew members had survived.

Grief-stricken relatives had gathered at Islamabad’s airport hoping for word on survivors. Six members of the Youth Parliament Pakistan had been on board. The United States Embassy here said two Americans had also been on the flight.

The Pakistani government declared that Thursday would be a national day of mourning for the crash victims.

Dawn Television reported that 100 bodies, many badly burned or mutilated, had been recovered by the afternoon. Officials said that cockpit recorders and the bodies of the pilots had been found. The plane, a 10-year-old Airbus A321 operated by a relatively new Pakistani airline, Airblue, was flying to Islamabad from Karachi .

In a country where terrorist activity has been rising — with repeated bombings attributed to Pakistani militants former focused solely on Kashmir or Afghanistan — officials said they had not ruled out the possibility of an attack. But the more immediate focus was weather.

Hashim Raza Garvaizi, a captain for Pakistan International Airlines, told GEO television that another flight had been diverted from the Islamabad airport because of the rain and fog just 30 minutes before the Airblue flight crashed.

Captain Garvaizi said that he knew the pilot and that he had an impeccable record. He speculated that the plane could have been struck by lightning or that wind currents could have caused it to dip lower than expected.

While the cause of the crash was not immediately clear, some Pakistani aviation experts said the crash may have been averted if the runways at Islamabad’s airport had a multi-directional instrument landing system, a ground-based tool common in developed countries, which precisely guides an aircraft through harsh weather.

But Mohammad Haroon, the managing director of Pakistan International Airlines and who has 34 years of flying experience, said that pilots regularly navigate the aircraft manually through bad weather. He said the cause of the crash was most likely to have been pilot error.

Express TV reported that the pilot received a warning that he was flying away from the runway.

The pilot responded, “I can see the runway.”

In a second exchange, the dispatcher advised, “Immediately turn left, Margalla [Hills] are ahead.”

The pilot responded, “we can see it,” according to Express TV.

An Airblue official identified one of the pilots as Pervaiz Iqbal Chaudhry and said he had more than 25,000 flying hours over a 35-year career.

Imtiaz Inayat Elahi, chairman of the Capital Development Authority, told Express TV that 150 rescuers had been sent to the crash site, in the Margalla Hills, where “it is difficult to work” because of harsh conditions and the densely forested terrain.

“Helicopters cannot just land there,” Mr. Elahi said.

Wednesday’s crash was the first fatal crash for Airblue, which began operating in 2004, according to a database of aviation crashes maintained by the Flight Safety Foundation. According to that database, which lists crashes dating to 1941, 54 people were killed in the crash of a Pakistan International Airlines flight in Bunji, in the far north, in 1989; 51 were killed in an Afghan Air Force crash at the Khojak Pass, near the western city of Quetta, in 1998, and 45 were killed in 2006 after a P.I.A. flight crashed after taking off from Multan, in the east. In a statement, Airbus said the twin-engine plane was built in 2000 and leased to Airblue in 2006, and had made a total of about 13,500 flights. Airblue said the plane had no history of problems.

Imran Abbasi, 23, was shopping at the foot of the hills when he noticed the aircraft “flying as low as a four-story building,” he said.

He said he continued to watch it for a few minutes.

“I could tell it was trouble because it stayed so low even though the mountains were up ahead,” he said in Islamabad.

As the aircraft started to turn, the right side of its front banged into the highest mountain, emitting an instant billow of blue fire and black smoke.

Mr. Abbasi said he did not hear or see any other explosion before the aircraft made contact with the mountain.

Mr. Abbasi then spent an hour and 15 minutes hiking to the top of the mountain to help rescue potential survivors. He said there was no path for the 300 or so volunteers who simply snaked their way through the forest by following the smell of “burning lard.”

When he arrived, he saw body parts everywhere.

“No one was intact, not even a whole head was intact,” he said.

NDTV, an Indian television station, carried a report from Islamabad of a woman who saw the plane, flying low, pass over her house just before the crash. The plane disappeared and she heard a loud explosion, she said.

“I don’t think they could see where they were going,” she said.

Another resident, Saqlain Altaf, told a local television station that he was on a family outing in the hills outside of Islamabad when he saw the airliner looking unsteady.

“The plane had lost balance, and then we saw it going down,” Mr. Altaf said.