People stand on the streets after evacuating their homes following an earthquake in Istanbul on Thursday. DHA / AP

A 5.7 magnitude quake shook buildings and damaged a mosque in Istanbul on Thursday, sending some residents rushing from buildings though there were no immediate reports of casualties.

Witnesses in Turkey's largest city felt buildings sway and said some offices and schools were temporarily evacuated.

The tremor was at a depth of 12.6 km, the Kandilli Observatory and Earthquake Research Institute said, locating its epicentre 70 km west of Istanbul in the Marmara Sea, south of the town of Silivri. It struck at 1:59pm.

Both the observatory and the US Geological Survey assessed its magnitude at 5.7.

"The quake really shook at the start and then it continued, maybe it felt like that because the building is so tall," said Ozge Etcan, 27, an employee at a financial institution in Istanbul.

City Mayor Ekrem Imamoglu said on Twitter there were no immediate reports of damage or people hurt.

CNN Turk broadcast video showing the top section of a minaret at the central mosque in Istanbul's Avcilar district had collapsed. It was not clear if the collapse caused any casualties or further damage.

In 1999, a quake measuring 7.6 struck the city of Izmit, 90 km southeast of Istanbul, killing more than 17,000 people.

The AFAD observatory and the Disaster and Emergency Management Directorate clocked Thursday's quake at 5.8 magnitude.

Reuters