The explosion in Istanbul occurred at about 10:20 a.m. local time this morning in Sultanahmet Square in Istanbul near the Obelisk of Theodosius, Hurriyet reports.
The explosion was heard in many of Istanbul's districts.
So far, reports say that ten people have been killed and 15 more injured.
Another photo from Istanbul's Sultanahmet district, the site of this morning's explosion.
CNN Turk is still reporting on the explosion in Istanbul despite a media blackout.
According to CNN Turk, police are focussing on the possibility that a suicide bomber was responsible for the blast.
German and Norwegian tourists are among those killed in the blast this morning at Istanbul's main tourist district, Euronews is reporting, saying that the victims were part of a tour group.
Turkish Interior Minister Efkan Ala has arrived at the Prime Minister's residence in order to brief Prime Minister Ahmet Davutoğlu on the attack in Sultanahmet, the state-run Anadolu Agency has reported.
Freelance journalist Zia Weise has posted this photo taken from a rooftop looking out toward Istanbul's Blue Mosque.
Istanbul's Blue Mosque has been completely closed off, says freelance journalist Zia Weise.
Two hours after the blast in Turkey's Sultanahmet district, Wall Street Journal reporter Ayla Albayrak says that tourists are still on the streets.
A TV report has said that a suicide bomber was responsible for the blast this morning in Istanbul, AP are reporting.