Thousands of Shiite pilgrims headed on foot to a north Baghdad shrine on Thursday to commemorate the death of a revered Shiite imam, undaunted by waves of attacks that killed 72 people.

Routes leading to the Kadhimiyah neighbourhood of north Baghdad, the site of the shrine of Imam Musa Kadhim, who died in 799 and was the seventh of 12 imams, were closed to all but emergency traffic, AFP correspondents reported.

Pilgrims, who were searched at multiple checkpoints on their way to Kadhimiyah, wound through the streets in their thousands under a blistering sun, repeating religious chants, with some beating their chests in a sign of mourning for the imam.

Tents along the way provided the pilgrims with free food and water, while some people set out small machines along the road that sprayed mist on the pilgrims to cool them as they passed.

Long lines of pilgrims, many wearing green headbands, the colour of Islam, and some carrying green flags with the image of Imam Kadhim, were seen in the Kadhimiyah area walking towards the shrine.

A car bomb exploded on the outskirts of Kadhimiyah on Wednesday, killing seven people, leaving a hole two metres (yards) deep in a street, damaging cars and destroying a number of makeshift houses.

Vast crowds of chanting pilgrims were seen walking through Karrada in central Baghdad, where a bomb on Wednesday blasted the pilgrims' food tents, killing 16 people, damaging cars and scattering human remains across the street.

"This is the sixth year I have come ... I left home around 2:00 am and I feel so good now," said Hussein Murawih, 17, who walked from Suwayrah, some 60 kilometres (40 miles) southeast of Baghdad.

"We just came to tell the terrorists that we are against you. We are not afraid of the explosions or of terrorism. Visiting Imam Kadhim is a great thing because we want to express condolences to the imam."

Another pilgrim also brushed off Wednesday's killings.

"The explosions mean nothing for us. It is not something new. Even if 20 car bombs exploded every day, does that mean we will stop walking to the imam? No," said Salam Jaber, 27.

"I have been walking for five days," said Jaber, who came from the town of Muwafaqiyah, some 180 kilometres (110 miles) southeast of Baghdad.

Coordinated attacks took place across Iraq on Wednesday, leaving a total of 72 people dead and more than 250 wounded, and marking the deadliest day in the country in almost 10 months.

Shiite pilgrimages were prohibited under the rule of Saddam Hussein, who was executed in 2006 after being overthrown in the US-led invasion of 2003.

Along with the security forces, the Shiite majority in Iraq has been a main target of Sunni Arab armed groups since the fall of Saddam's Sunni-dominated regime.

Violence across Iraq has declined dramatically since the 2006-2007 peak of sectarian bloodshed but attacks remain common, especially in Baghdad. A total of 132 Iraqis were killed in May, official figures show.