ISTANBUL, Turkey (AP) _ A strong earthquake struck western Turkey today, collapsing buildings already damaged in a deadly quake last month and killing at least six people and injuring more than 200, officials said.

Most of the injured suffered broken bones as they jumped from buildings.

The 2:55 p.m. quake had a preliminary magnitude of 5.8 and was centered on Izmit, about 50 miles southeast of Istanbul, the city's Kandilli Observatory reported.

The U.S. Geological Survey in Golden, Colo., also reported that the quake registered a preliminary magnitude of 5.8, and called it an aftershock to the August quake.

``It was the strong aftershock which had been expected,'' agreed Aykut Barka, professor of geology at Istanbul Technical University.

Istanbul Deputy Governor Ali Cafer Akyuz said three people were killed in the town of Kocaeli when a building collapsed on their car. Another three were killed in the same town when a building fell on them, he said.

The semi-official Anatolia news agency had reported previously that two people were killed. It was not clear if they were in addition to or included in the toll announced by Akyuz.

Prime Minister Bulent Ecevit said 239 people were hurt. Injuries were reported in the towns of Adapazari, Kocaeli, Golcuk and Izmit, which had suffered serious damage in the August quake.

There were reports of traffic jams in Izmit as frightened residents tried to flee the city.

Ecevit immediately suspended classes in the area hit by today's quake. Schools had reopened throughout Turkey today after summer recess.

Today's jolt was felt as far away as Istanbul, where people rushed into the streets in panic. Telephones lines in Istanbul were down after the quake.

Last month's quake, which registered 7.4, killed more than 15,000 people and devastated western Turkey, the country's industrial heart.