An earthquake measuring 4.2 on the Richter scale hit Istanbul early Friday, injuring four people, the seismological observatory here announced.
The quake's epicenter was recorded some 10 kilometres (six miles) south of Istanbul in the Marmara Sea, the Bosphorus University observatory said
The four injured people were hurled out of windows of their homes in coastal areas, CNN-Turk reported.
"It could be a preliminary tremor before a bigger quake," engineer and geophysicist Mehmet Ercan told the television channel. A major earthquake measuring between 6.3 and 7.2 on the Richter scale could be on the way, he added.
Friday's quake struck in the middle of the night and roused residents of this city of more than 12 million inhabitants. But there was no evident panic.
Turkey is a highly earthquake-prone country that is almost criss-crossed by faultlines.
Two huge tremors struck northwestern Turkey in August and November last year, killing nearly 20,000 people -- ISTANBUL (AFP)
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