A powerful 7.6-magnitude earthquake struck Costa Rica's Pacific coast Wednesday, killing at least one person, briefly knocking out power and phone lines, and triggering tsunami warnings, authorities said.

Trees fell, rooftops were damaged and roads split by the quake near the epicenter in the coastal province of Guanacaste. People rushed into the streets 150 kilometers (95 miles) away in the capital San Jose.

Authorities said around 20 people were injured in the quake. Nearly 12 hours after the quake, some towns remained without electricity or water.

A Red Cross spokesman initially said a man and a woman died after suffering heart attacks in the town of Filadelfia, not far from Nicoya, which is roughly 10 kilometers (six miles) from the epicenter.

But the Red Cross later corrected this to say just one person, a 55-year-old woman, had died of a heart attack.

"Here in Nicoya, fortunately we have only seen very minor injuries, people with minor cuts -- nothing significant given the magnitude of the storm," said the spokesman, Adolfo Saenz.

Costa Rican President Laura Chinchilla said: "The most important thing is to remain calm, there is no major damage."

The US Geological Survey initially said the quake, which struck on the Pacific coast of Costa Rica, measured 7.9 on the Moment Magnitude Scale, but revised both the intensity and location in a subsequent advisory.

In its latest advisory, the USGS said the quake measured 7.6 and struck at a depth of about 40 kilometers.

A USGS map showed the quake centered near the Pacific coast, in picturesque Guanacaste, a tourist area popular for its cliffs, beaches and surfing.

A tsunami warning was issued for Costa Rica, Panama and Nicaragua, but later cancelled, the US Pacific Tsunami Warning Center said. Initially, the warning had extended from Mexico to Peru.

"We felt it very strongly, and ran, afraid that the house was going to come down. People are very alarmed," a Nicoya resident told a local radio station.

The quake was so strong the peninsula heaved up by nearly one meter, said Marino Protti of Ovsicori, a government geological observatory. He said that in coming days there could be aftershocks measuring 7.

The country is used to seismic activity but people in the area were stunned by the strength of the quake.

"We were in the pool. And a wave rose up in the pool," one nervous tourist said on television in Pinilla, near the quake's epicenter.

In San Jose, some buildings and schools were evacuated. Many areas of the capital also lost power and cellular phone service for a brief period.

Thousands of people abandoned buildings on San Jose's downtown Paseo Colon, and gathered outside for at least an hour as a precaution.

Small landslides were reported on the highway that links the capital to the Pacific coast, but none was large enough to block vehicles.

As calm eventually returned, helicopters buzzed overhead with experts evaluating the damage. The Red Cross office in Panama said it was also sending a chopper and a team of disaster relief experts.

The quake was felt strongly in neighboring Nicaragua, Panama and El Salvador.

In San Salvador, civil protection agency spokeswoman Glenda Duran told AFP that first responders had been put on alert.

"The order is that the population in coastal areas get away from beaches to secure zones over the next three hours," she said.

Panama's director for civil protection, Arturo Alvarado, told CNN that the quake was felt most strongly in a border region with Costa Rica.

"It's a very strong quake. We pray to God that there is no damage," he said.

In February 2010, a massive 8.7-magnitude quake earthquake hit Chile's central Maule region, south of Valparaiso, generating tsunami waves, killing more than 500 people and causing billions of dollars in damage.