BOGOTA, Colombia (CNN) -- A strong earthquake shook western Colombia on Monday afternoon, killing at least 273 people and wounding more than 900 in the nation's coffee-growing belt, Colombian officials said.

The quake, given a preliminary magnitude of 6 by the U.S. Geological Survey in Golden, Colorado, was centered in Valle del Cauca state, 220 kilometers (140 miles) from the capital, Bogota.

The death and damage toll appeared to be highest in three cities near the epicenter -- Armenia, Pereira and Calarca.

Television footage showed people crushed under the rubble of collapsed buildings. Residents frantically tried to rescue victims trapped below the debris of a fallen building in Armenia, capital of Quindio state.

"There's no way to measure this crisis," said Armenia Mayor Alvaro Pulido. Radio reports said several buildings on the city's main plaza, including a bank and police barracks, had collapsed. Pulido said thousands of people were left homeless.

City officials declared a dawn-to-dusk curfew in Pereira and Armenia to allow rescue teams to work unhampered. Authorities also were reported to have cut off power supplies in both cities, fearing electricity could spark fires in damaged buildings.

The quake was felt through most of the country, sending tall buildings swaying in Bogota and in the northwest industrial center of Medellin.

Colombian President Andres Pastrana delayed a trip to attend a World Bank meeting in Germany and instead flew to Pereira.

Monday's quake was the worst to hit Colombia since a 1983 tremor struck the city of Popayan, in southwest Cauca province, killing more than 300 people.

The Associated Press and Reuters contributed to this report.