JAKARTA, Indonesia â€"  A strong earthquake off Indonesia's coast caused tall buildings to sway in the capital Monday afternoon, but officials said there was no threat of a tsunami.

No damage or casualties were immediately reported.

Indonesia's Meteorology and Geophysics Agency put the preliminary magnitude of the quake at 6.1. It hit 121 kilometers (75 miles) southwest of Sukabumi, a town on the coast of West Java province. It was centered 24 kilometers (15 miles) beneath the floor of the Indian Ocean.

Office workers in high-rise buildings felt about 10 seconds of intense shaking.

Jakarta has a population of 9 million. Indonesia has frequent earthquakes due to its location on the Pacific "Ring of Fire," an arc of volcanos and fault lines encircling the Pacific Basin.