Police officers detain Istanbul blast suspect, Syrian woman named Alham Albashir, on Monday. AFP / Reuters

Turkey on Monday accused a Syrian woman of planting a bomb that killed six people in Istanbul, blaming the outlawed Kurdistan Workers' Party (PKK) of carrying out the attack.

Two girls, aged nine and 15, were among those killed when the bomb exploded shortly after 4:00pm on Sunday in Istiklal Avenue, home to smart boutiques and European consulates. More than 80 other people were wounded.

"The person who planted the bomb has been arrested," Interior Minister Suleyman Soylu said in a statement broadcast by the official Anadolu news agency early Monday.

"According to our findings, the PKK terrorist organisation is responsible," Soylu said.

Police, quoted by private NTV television, said the chief suspect is a Syrian woman working for Kurdish militants. Forty-six people were detained in total, police said.

Soylu said the order for the attack on Istanbul's Istiklal Avenue was given in Kobani, a city in northern Syria, where Turkish forces have carried out operations against the Syrian Kurdish YPG militia in recent years.

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"We have evaluated that the instruction for the attack came from Kobani," Soylu said, adding that bomber had passed through Afrin, another region in northern Syria.

"The person who carried out the incident, left the bomb, was detained. Previously, around 21 other people had been detained," Soylu said.

Members of the forensics pack a baby trolley near the scene of an explosion in Istanbul, Turkey, on Sunday. Reuters

Television news reports showed images of a person, who appeared to be a woman, leaving a package below a raised flower bed in Istiklal Avenue, a popular spot for shoppers and tourist, with a tramline running the length of the street.

Fifty people were discharged from hospital after Sunday's attack, which sparked concerns that Türkiye could be targeted with more bombings and attacks, like the series of attacks that it suffered between mid-2015 and 2017.

Istanbul has been targeted in the past by Kurdish, Islamist and leftist militants. An offshoot of the Kurdistan Workers Party (PKK) claimed twin bombings outside an Istanbul soccer stadium in December 2016 that killed 38 people and wounded 155.

Of those wounded on Sunday, two of the five people being treated in intensive care were in a critical condition, the Istanbul Governor's Office said. They were among the 31 wounded still in hospital.

Municipal workers clean debris as Turkish policemen secure the area in Istanbul on Sunday. AFP

Hundreds of people fled the historic Istiklal Avenue after the blast on Sunday, as ambulances and police raced in. The area, in the Beyoglu district of Türkiye's largest city, had been crowded as usual at the weekend with shoppers, tourists and families. Ankara says the YPG, which Washington has supported in Syria, is a wing of the PKK.

People leave the area after an explosion on Istanbul’s popular pedestrian Istiklal Avenue, Istanbul. AP

Condemnations of the attack and condolences for the victims poured in from several countries including the UAE, Azerbaijan, Britain, Egypt, Greece, Italy, Pakistan and Ukraine.

Reuters / AFP