An earthquake measuring 5.2 on the open-ended Richter scale struck the bay of Gemlik, north-western Turkey, on Tuesday evening, the Kandilli Observatory in Istanbul reported.
There were no immediate reports of casualties or damage, but panicked residents took to the streets of Gemlik town, which is about 100 kilometres (63 miles) south of Istanbul, where the quake was also felt.
"We really felt it," an Istanbul resident told AFP by telephone. "I had to throw myself under a table."