They said bin Laden's guards opened fire from the roof of the compound in the small northwestern town of Abbottabad, and one of the choppers crashed. However U.S. officials said no Americans were hurt in the operation. The sound of at least two explosions rocked Abbottabad as the fighting raged.
Abbottabad is home to three Pakistan army regiments and thousands of military personnel and is dotted with military buildings. The discovery that bin Laden's was living in an army town in Pakistan raises pointed questions about how he managed to evade capture and even whether Pakistan's military and intelligence leadership knew of his whereabouts and sheltered him.
Critics have long accused elements of Pakistan's security establishment of protecting bin Laden, though Islamabad has always denied this. Army and government officials gave no formal comment Monday.
Most intelligence assessments believed bin Laden was holed up somewhere along the lawless border area between Pakistan and Afghanistan, possibly in a cave and sheltered by loyal tribesmen. That region is remote, homes to soaring mountains and the Pakistan state has little or no presence in much of it.
It was not known how long bin Laden had been in Abbottabad, which is surrounded by hills and is less than half a days drive from the border region with Afghanistan and two hours from the capital, Islamabad.
It was also unclear how much of a role - if any - Pakistani security forces played in the operation. A Pakistani official said the choppers took off from Ghazi air base in northwest Pakistan, where the U.S. army was based to help out in the aftermath of the floods in 2010.
Pakistani officials said a son of bin Laden and three other people were killed.
Other unidentified males were taken by helicopter away from the scene, while four children and two woman left in an ambulance, the official said.
Abbottabad resident Mohammad Haroon Rasheed said the raid happened about 1:15 a.m. local time.
"I heard a thundering sound, followed by heavy firing. Then firing suddenly stopped. Then more thundering, then a big blast," he said. "In the morning when we went out to see what happened, some helicopter wreckage was lying in an open field."
He said the house was 100 meters (yards) away from the gate of the Kakul Military Academy, an army run institution where top officers train. A Pakistan intelligence official said the property where bin Laden was staying was 3,000 square feet.
A Pakistani official in the town said fighters on the roof opened fire on the choppers as they came close to the building with rocket propelled grenades. Another official said four helicopters took off from the Ghazi air base in northwest Pakistan.
Last summer, the U.S. army was based in Ghazi to help out in the aftermath of the floods.
The officials spoke on condition of anonymity because of the sensitivity of the information.
Pakistan has in the past cooperated with the CIA in arresting al-Qaida suspects on its soil, but relations between its main intelligence agency and the CIA had been very strained in recent months amid tensions over the future of Afghanistan.
In late January, a senior Indonesian al-Qaida operative, Umar Patek, was arrested at another location in Abbottabad.
News of his arrest only broke in late March. A Pakistani intelligence official said its officers were led to the house where Patek was staying after they arrested an al-Qaida facilitator, Faisal Shahzad, who worked at the post office there.