A magnitude-6.7 earthquake struck Wednesday off Costa Rica's Pacific coast, the Ovsicori seismological observatory said, but authorities here discounted the risk of a tsunami, despite a warning issued by the U.S. Geological Survey.

"Geologists and oceanographers with the CNE (emergency management agency) rule out a risk of tsunami on the country's coasts. They urge residents to remain calm," President Laura Chinchilla said on Twitter.

Two people were reported missing after the quake, whose epicenter was located beneath the ocean floor about 13 kilometers (8 miles) from the northern coastal town of Gangrejal de Nicoya.

The U.S. Geological Service initially estimated the magnitude of the temblor at 7.9 - later reduced to 7.6. - and issued a tsunami warning for the Pacific coasts of Central America and Mexico.

The USGS alert was subsequently narrowed to Costa Rica, Nicaragua and Panama.

The quake was felt strongly here in San Jose, prompting evacuations at some buildings.

Television stations aired footage of structural damage on the Pacific coast and roads blocked by landslides. EFE