Dozens of attacks across Iraq, including a brazen car bombing on the way to Baghdad airport, killed 50 people on Monday, just days before the country's first elections since US troops withdrew.

The violence, which mostly struck during morning rush hour amid tightened security ahead of the polls, also wounded nearly 300 people and raises further questions about the credibility of the April 20 vote, seen as a key test of Iraq's stability and its security forces' capabilities.

A total of 14 election hopefuls have already been murdered and just 12 of the country's 18 provinces will be taking part in the vote.

Officials said more than 30 bombings and a shooting hit 12 different areas of Iraq, leaving 50 people dead and making Monday the country's deadliest day since March 19.

No group immediately claimed responsibility for the attacks, but Sunni militants linked to Al-Qaeda frequently attack both government targets and civilians in a bid to destabilise the country, and they have reportedly sought to intimidate candidates and election officials ahead of polling.

The deadliest attacks were in Baghdad, where eight bombings struck in seven neighbourhoods across the capital despite tougher checkpoint searches and heightened security.

Among them was a car bomb in a parking area used by vehicles making their way to Baghdad's heavily-guarded airport, a rare bombing on the road famously known as "Route Irish".

The airport road was once referred to by American forces as "RPG alley" for the high numbers of attacks there, but it has since become far more secure.

"There were several people, buses and private cars in the parking area when the explosion went off," said a man who gave his name as Abu Ali, at the site of the blast.

"It happened all of a sudden, and several people were killed and wounded. Some of the buses went straight to the airport to avoid more attacks."

In all, 30 people were killed and 92 wounded in the capital, officials said.

AFP journalists in Baghdad reported that sites of attacks were cordoned off by security forces who barred journalists from filming or taking photos of the aftermath of the bombings.

In Tuz Khurmatu, 175 kilometres (110 miles) north of Baghdad, six people were killed and 67 wounded by three near-simultaneous car bombs, and in Kirkuk, five people were killed and 44 wounded by six more car bombs.

Attacks elsewhere killed nine people and wounded 92 others.

Kirkuk and Tuz Khurmatu lie at the centre of a tract of disputed territory that stretches from Iraq's eastern border with Iran to its western frontier with Syria.

The swathe of land is claimed by both the mostly Arab government in Baghdad and the three-province autonomous Kurdistan region of north Iraq.

The dispute is often cited by officials and diplomats as the greatest long-term threat to Iraq's stability.

Soldiers and policemen cast their ballots for the provincial elections on Saturday, a week ahead of the main vote, the country's first since March 2010 parliamentary polls.

It is also the first election since US troops withdrew from Iraq in December 2011.

The election also comes amid a long-running crisis between Prime Minister Nuri al-Maliki and several of his erstwhile government partners, which officials and diplomats say insurgent groups exploit by using the political differences to enhance their room for manoeuvre on the ground.

More than 8,000 candidates are standing in the elections, with 378 seats on provincial councils up for grabs. An estimated 16.2 million Iraqis are eligible to vote.

Although security has markedly improved since the height of Iraq's confessional conflict in 2006-2007, 271 people were killed in March, making it the deadliest month since August, according to AFP figures.