A suicide truck bomb attack claimed by the Islamic State group killed 47 people at a crowded checkpoint south of Baghdad Sunday, the deadliest such attack in Iraq this year.

The massive blast completely destroyed the checkpoint manned by security forces guarding the northern entrance to Hilla, an area that had recently been spared such attacks.

"The suicide bomber used an explosives-laden truck, at a time when there was dense traffic," Faleh al-Radhi, the head of the security committee at Babil provincial council, said.

A doctor at Hilla hospital put the number of people killed by the blast at 47, including around 20 members of the security forces, and said at least 72 people were also wounded.

Radhi and police officers confirmed the casualty toll, the heaviest from any car bomb attack in Iraq this year.

The blast went off at around 1:00 pm (1000 GMT), a time of day when vehicles are usually bumper-to-bumper, waiting to be checked by security personnel.

An AFP photographer at the scene said that there was almost nothing left of the checkpoint.

He said one distraught man was asking rescuers, survivors and journalists to help him retrieve the body of his baby child from under the mangled wreckage of a car.

"When I got to the scene, there were people whose clothes were still on fire, they were screaming," said Hamza Kadhem, a 35-year-old labourer who was near when the blast went off.

The doctor at Hilla hospital said at least 11 of the wounded were in a very serious condition.

- Scenes of chaos -

Mohammed Jamal, a 27-year-old civil servant, was sitting in traffic when the explosion ripped through the lines of vehicles.

"My car windows just shattered with the blast," he told AFP from the emergency ward.

"After that, I can't remember much, I was lost in this chaos and found myself at Hilla hospital, I'm not sure how," he said.

Karim Sahi, 35, a taxi driver reached by phone, was also close to the checkpoint.

"When we heard the blast, we rushed to the scene. There were bodies everywhere, people running in all directions, some just froze there, screaming," he said.

A March 2014 suicide bombing at the same checkpoint outside Hilla, 80 kilometres (50 miles) south of the capital, killed 50 people and wounded more than 150.

The Islamic State group has not had fixed positions south of Baghdad since security forces and allied militias began their fightback against the jihadists in late 2014.

When Iraqi forces began their counter-offensive against IS, securing the Shiite shrine cities of Najaf and Karbala, south of Baghdad, was a priority.

The jihadist group has since been losing territory in Iraq. In the most recent operation, Iraqi forces have been retaking areas west of the city of Samarra and are continuing to advance.

In the cities IS retains control over, internal tension appears to be on the rise and the lack of supplies is taking its toll.

Observers have warned that, as its self-proclaimed "caliphate" shrinks towards extinction, IS will likely revert to its old guerrilla tactics and ramp up suicide car bomb attacks on civilian targets.

"The Rafidha (a derogatory term for Shiites) must understand that the battle has just begun and that the worst is yet to come," IS said as it claimed Sunday's bombing.

The attack on Hilla checkpoint was one of the deadliest bombings since a suicide explosion killed nearly 100 people in Diyala province, north of Baghdad, in July 2015.