ISLAMABAD: A car bomb destroyed a packed Pakistani market on Wednesday, slaughtering 80 people and underscoring the blood-drenched scale of the extremist threat as US Secretary of State Hillary Clinton visited.

Clinton, vowing new investments while fending off fierce Pakistani criticism of Washington's policies, arrived in Islamabad just hours before bombers unleashed one of the nuclear-armed nation's deadliest attacks in Peshawar.

"Eighty people have been killed and 200 wounded in this blast," North West Frontier Province information minister Mian Iftikhar Hussain told reporters at the bomb site in the volatile northwest city.

Doctors at Peshawar's Lady Reading Hospital said most of the dead were women and children, as a routine day out at the crowded bazaar ended in horror. The hard-pressed medics appealed to the public for blood donations.

"It was a car bomb. Some people are still trapped in a building. We are trying to rescue them," bomb disposal official Shafqat Malik told reporters.

The bomb in Peshawar, which lies on the edge of Pakistan's tribal badlands, trapped people under pulverised shops.

Flames leapt out of burning wreckage and smoke billowed in the air as one building collapsed into dust and rubble. Police evacuated panicked residents from the smouldering wreckage and firemen hosed down the flames.

"There are body parts. There are people. There are burnt people. There are dead bodies. There are wounded," said one doctor, Muslim Khan.

Clinton is the most senior US official to visit since US President Barack Obama put Pakistan at the heart of the fight against Al-Qaeda and made the war in neighbouring Afghanistan a top priority.

"We are turning a page on what has been in the last several years primarily a security, anti-terrorist agenda," Clinton told reporters travelling with her.

"It remains a very high priority. But we also recognise that it's imperative that we broaden our engagement with Pakistan," she added, pledging that the United States wanted to "strengthen democracy" and civilian institutions. US stands 'shoulder to shoulder' with Pakistan

Her arrival comes at a critical juncture for Pakistan, where a rising number of audacious attacks has shown Al-Qaeda and Taliban-linked extremists can target anyone at anytime, and with the military pressing a major offensive.

The Pakistan-US alliance can be uneasy particularly among the general public in both countries. The United States, which is heavily committed in Afghanistan, relies on Pakistan for regional stability and to fight militants.

Pakistan, whose cash-strapped government presides over a battered economy, relies on US cash and weapons to fight against extremism and militancy.

Clinton acknowledged there can be "misunderstanding" and "miscommunications", but stressed that the Obama administration was committed to building a long-term relationship with the troubled country.

"Nine months is not a long period of time to turn around a relationship that has a lot of scars," she said.

"It's fair to say that we have really increased the level of conversation and sharing of information over nine months," Clinton said.

The United States is keen to bolster the civilian government, whose relations with the powerful military have been fraught, following on from a massive 7.5 billion dollar non-military aid package already signed into law.

The military and political opposition slammed the package -- designed to help Pakistan fight Islamist insurgency by building schools, training police and strengthening democracy -- for allegedly violating Pakistan's sovereignty.

Clinton said she was "concerned" by the opposition and reiterated that the bill imposed no conditions on Pakistan, pledging further assistance.

"We will be making some announcements about some of the investments we are making with Pakistan on the civilian side," she added referring to jobs, reliable sources of energy, education and healthcare.

Around 30,000 troops are pressing an assault against Pakistani Taliban fighters holed up in South Waziristan, part of the tribal belt on the Afghan border where US officials say Al-Qaeda is plotting attacks on the West.

Clinton said it was "important to recognise the high price the Pakistanis are paying" in the war on Islamist militancy.

"They (the military) are extraordinarily committed and we have to support them the way we can," said Clinton, who is expected to meet some of the more than 200,000 people who have been displaced by the latest offensive.