A strong earthquake of magnitude 8.1 has struck off southern Mexico, killing at least five people.
The epicentre was in the Pacific, about 87km (54 miles) south-west of the town of Pijijiapan and at a depth of 70km, the US Geological Survey said.
A tsunami warning has been issued for Mexico, Guatemala, El Salvador, Costa Rica, Nicaragua, Panama and Honduras.
The quake was felt in Mexico City, with buildings swaying and people running into the street.
The tremors there, about 1,000km from the epicentre, were reported to have lasted up to a minute.
Two deaths were reported in Mexico's Chiapas state, closer to the epicentre, and two more in Tabasco state.
Guatemala's president also reported at least one death in his country.
Severe damage was reported to buildings in southern Mexico and in Guatemala.
The Pacific Tsunami Warning Center said that tsunami waves "reaching more than three metres above the tide level are possible along the coasts of Mexico". There is a coastal evacuation in Chiapas state.
Mexican President Enrique Peña Nieto tweeted that he was in contact with the country's centre for disaster prevention. Schools have been closed in Mexico City and Chiapas state.
If confirmed at magnitude 8.1, the quake would be bigger in strength to those that struck Mexico in 1995 and 1985. The latter hit close to Mexico City and caused thousands of deaths.
The Mexican interior ministry has given the latest quake a higher magnitude, of 8.4, which would be the highest the country has ever recorded.
A series of aftershocks ranging from 4.3 to 5.7 in magnitude have been recorded closer to the Mexican coast, off the town of Paredon.
Some electricity cuts have been reported in the capital and social media video showed lampposts swaying violently, but there are no reports of major damage there.
Journalist Franc Contreras, who is in Mexico City, told the BBC: "You could hear loud cracks in the concrete. It sounded like a giant wooden branch being just broken open violently.
"People were streaming out of the hallways here. And everybody walking out single file into the streets, trying to avoid overhead high power lines."
Guatemalan President Jimmy Morales appealed for calm on national television and in a Twitter post.
"We have reports of some damage and the death of one person, even though we still don't have exact details," Associated Press quoted Mr Morales as saying.
No tsunami warning has been issued for the US west coast.
Mexico is currently also being threatened on its eastern coast by Hurricane Katia.
The category one hurricane is about 300km south-east of Tampico and has sustained winds of 140km/h the National Hurricane Center says.