A strong earthquake shook the Romanian capital Bucharest on Wednesday night, rattling buildings and sending objects flying off shelves, witnesses said. Police and health officials said it was too soon to say if there had been any casualties. The U.S. Geological Survey said a preliminary estimate put the quake's magnitude at six. It had no immediate reports of damage but a spokesman said a tremor of that magnitude was capable of causing a lot of damage, especially if it was near an urban area. An official at Romania's main seismic centre in Vrancea, about 250 km (155 miles) north of Bucharest, said: "It was strong, we estimate around six (magnitude)." The official said there was no official measurement yet because the quake was still rumbling. The U.S. experts said the quake was centred about 140 km (85 miles) north-northeast of Bucharest. Television stations interrupted their regular programmes to say a "very strong" quake had struck Romania and that it was felt especially strongly in Bucharest.