* Worst quake in Guatemala in 36 years
* President says 100 missing, death toll could rise
A strong earthquake off the coast of Guatemala shook buildings in the capital and killed at least 18 p e ople On Wednesday, trapping others under rubble and triggering evacuations as far away as Mexico City.
The 7.4 magnitude quake hit at 10:35 a.m. local time (1635 GMT). A local fire chief said the dead were buried under rubble in tw o d ifferent Guatemalan towns in the mountainous region near the Mexican border.
Landslides were blocking roads in some areas, authorities said, and about 40 houses were severely damaged.
It was the strongest earthquake to hit Guatemala since a 7.5 magnitude quake in 1976 that claimed more than 20,000 lives.
President Otto Perez said that as many as 100 people were unaccounted for, based on reports from relatives.
"These are preliminary figures and we don't have them confirmed," Perez said in Guatemala City. "Our priority is to focus on lives, rescuing people and treating the wounded."
He said there had been five aftershocks. Local fire chief C ecilio Chacaj s aid the bodies of the 18 dead had been pulled from rubble in the towns of San Marcos and Quetzaltenango.
The quake struck off Guatemala's Pacific coast, 15 miles (24 km) south of Champerico and 101 miles (163 km) west-southwest of the capital, the U.S. Geological Survey said.
Evacuations in Guatemala City filled the streets with office workers calling friends and relatives on their cell phones, b ut people soon returned to work.
"It was really big; I felt quite nauseous," said secretary Vanessa Castillo, 32, who was evacuated from her 10th floor office in Guatemala City.
Building janitor Jorge Gamboa said: "I was in the bathroom. When I came out the office was empty and I thought, what's happening? They didn't even say goodbye."
The epicenter was 26 miles (42 km) below the surface, according to the USGS, which initially reported the quake as magnitude 7.5.
The quake was also felt in El Salvador and more than 765 miles (1,232 km) away in Mexico City, w here some p eople also fled offices and homes. M ayor Marcelo Ebrard said the quake was felt strongly in a large part of the city of 20 million people.
The Pacific Tsunami Warning Center said a very small tsunami was registered on Guatemala's coast, adding there was a risk of localized damage within a 62 mile (100 km) radius.