Heavily armed militants stormed a Pakistani air force base on Thursday, sparking clashes that left nine people dead and raised concerns about the safety of the country's nuclear arsenal.

One security official was killed and a plane damaged in the pre-dawn assault at PAF Base Minhas, where suspected Islamists again showed their ability to penetrate a sensitive military site five years into a Taliban insurgency.

There has been a lull in recent attacks, but speculation is now heavy that Pakistan could bow to US demands for an operation against militants in their premier fortress of North Waziristan, in the tribal belt on the Afghan border.

An official denied there were nuclear weapons on the heavily guarded base, but the audacious assault would likely raise further questions in the west about the dangers of Pakistan's atomic weapons falling into extremists' hands.

The air force said seven to eight attackers dressed in military uniforms and armed with with rocket propelled-grenades and suicide vests struck the base and adjacent Pakistan Aeronautical Complex at 2am.

The complex assembles Mirage and, with Chinese help, JF-17 fighter jets.

"Other miscreants then fired RPGs from outside the base boundary wall," said the air force, adding that one aircraft had been damaged.

PAF Minhas, in the town of Kamra in Punjab province 60 kilometres (35 miles) northwest of Islamabad, has been attacked twice before.

Witnesses said the attackers came round the back, exploiting the holiest night of the Muslim fasting month of Ramzan to remain undetected as long as possible.

"Most of the male residents (from the village at the back) were in mosques for special prayers," local resident Athar Abbas told Express Television.

"I heard three or four explosions, there was heavy gunfire also," he said. "It appears that the militants arrived using a village track and climbed over the wall."

One officer said that he saw flames after waking up for his late night meal, eaten during the dawn-to-dusk Muslim fasting month.

"There was an announcement by megaphone for soldiers not to move from the barracks and we were forbidden from going to the area where I saw the fire," he said. Special forces and police were scrambled to the scene.

Air Force spokesman Tariq Mahmood said eight attackers and one security official had been killed, and the base commander wounded in the shoulder, but by mid-morning still stopped short of confirming that the base was clear.

A helicopter flew overhead and the military said at least two remote-controlled bombs were discovered and destroyed during searches of the base.

There was no immediate claim of responsibility but the Pakistani Taliban have targeted a string of military bases since rising up against the government in July 2007.

In May 2011, it took 17 hours to quell an attack on an air base in Karachi claimed by the Taliban, piling embarrassment on the armed forces just three weeks after US troops killed Osama bin Laden in Pakistan.

Thursday's attack was the second in weeks to see troops die near the relatively secure capital. Gunmen on July 9 killed seven security personnel who had camped by a river less than 160 kilometres (100 miles) southeast of Islamabad.

Pakistan has been on alert for independence day on Tuesday and the Muslim festival of Eid, which is expected to begin at the weekend.

On Tuesday, the head of the army, General Ashraf Kayani, used his independence day address to describe the war on terror as "our own war and a just war too" -- not an American conflict as often portrayed.

He said "no state can afford a parallel system of governance and militias", and called on the nation to stand united or face the risk of a "civil war situation".

Pakistan says 35,000 of its people, including more than 3,000 soldiers, have been killed as a result of terrorism since the 9/11 attacks and the 2001 US-led invasion of neighbouring Afghanistan.

The base in Kamra was previously targeted on October 23, 2009 when a suicide bomber killed six civilians and two Pakistan air force personnel at a checkpoint.

On December 10, 2007, at least five children of base employees were wounded when a suicide car bomber struck a school bus.