Up to 1,000 Iraqis died in a gruesome stampede today when rumours of an imminent suicide bombing attack sparked panic on a crowded bridge in Baghdad.

The most deadly single incident since the Iraq war began two years ago saw hundreds trampled underfoot or drowning in the muddy Tigris - including children thrown from the bridge by the parents to avoid the crush.

Men waded into the water to pluck out bodies, which piled up at hospitals around the Iraqi capital. The death toll is expected to reach 1,000, a manager at Iraq’s Health Ministry said. “An hour ago the death toll was 695 killed, but we expect it to hit 1,000,” Dr Jaseb Latif Ali told the Reuters news agency.

"This appears to be an accident, a crush of humanity, where the weakest couldn't survive. The bridge is now littered with shoes abandoned by pilgrims," Richard Beeston, Diplomatic Editor of The Times, said from Baghdad.

"One thing we're absolutely sure of is that the casualty toll is enormous. It seems to be building up to be the worst tragedy in Iraq since the war and that's really saying something."

Tens of thousands of Shia Muslim pilgrims were crossing the al-Aima bridge heading towards the Imam Mousa al-Kadim shrine for the annual commemoration of the death of the ninth century Shia martyr. Local television reports said a million Shia pilgrims were joining the procession.

But the crowd had already come under mortar fire from Sunni insurgents - who were in turn attacked by US forces on Apache helicopter gunships. Seven people were reported to have been killed in a three separate mortar attacks two hours before the bridge disaster.

Beeston said that the crowd on the bridge had been crossing from a mainly Sunni neighbourhood but was bottlenecked around a tight police checkpoint set up to prevent a repeat of suicide attacks against the mosque. Everyone passing through the checkpoint was being searched.

"This created a chokepoint at the bridge and people were crushed to death," Beeston said. "Children were thrown over the side of the bridge by their parents, who did not want them to be crushed. Most of the killed were children or old people, who couldn't stand and were crushed or trampled."

State television said that Ibrahim Jaafari, the Prime Minister, declared three days of mourning. After the disaster, thousands of people rushed to both banks of the river searching for survivors. Hundreds of men stripped down and waded into the muddy water downstream from the bridge trying to extract past.

Victims were transported to various hospitals and officials themselves were scrambling to compile an accurate count.

Hussein Ali Kamal, the Deputy Interior Minister, said the death toll stood at least 640 but the figure could rise. Survivors were rushed in ambulances and private cars to numerous hospitals and officials were scrambling to compile an accurate picture of casualties.

"We were on the bridge. It was so crowded. Thousands of people were surrounding me," said survivor Fadhel Ali, 28, as he stood bare-footed and soaking wet after swimming from the river.

"We heard that a suicide attacker was among the crowd. Everybody was yelling so I jumped from the bridge into the river, swam and reached the bank. I saw women, children and old men falling after me into the water."

Abdul-Mutalib Mohammed, the Health Minister, told state-run Iraqiya television that there were "huge crowds on the bridge and the disaster happened when someone shouted that there is a suicide bomber on the bridge".

"This led to a state of panic among the pilgrims and they started to push each other and there was many cases of suffocation," he said.

At least six other people died after drinking poisoned juice and food they received around the mosque, Dr Muhannad Jawad of the Yarmouk hospital said.

Shia religious festivals have often been targeted for attack by Sunni extremists seeking to trigger civil war among the rival communities. In March last year suicide attackers struck worshippers at the same Baghdad shrine and a holy site in Karbala, killing at least 181 overall.

The head of the country’s major Sunni clerical group, the Association of Muslim Sholars, told Al-Jazeera television that the disaster was "another catastrophe and something else that could be added to the list of ongoing Iraqi tragedies".

"On this occasion we want to express our condolences to all the Iraqis and the parents of the martyrs, who fell today in Kazimiyah and all over Iraq," the cleic, Haith al-Dhari, said.

Times Recommends

• 'Great Schlep' may seal deal for Obama
• Hindu 'storm troopers' flex their muscles
• Ahtisaari: deserved reward for (failed) plan