A local fire chief said the dead were buried under rubble in three different Guatemalan towns. It was the strongest earthquake to hit Guatemala since a 7.5 magnitude quake in 1976 that claimed more than 20,000 lives.
Landslides were blocking roads in some areas, authorities said, and about 40 houses were severely damaged after the 7.4 magnitude earthquake hit at 10:35 a.m. local time (1635 GMT).
The quake struck off Guatemala's Pacific coast, 15 miles (24 km) south of Champerico, Guatemala, and 101 miles (163 km) west-southwest of the capital, the US Geological Survey said.
A Reuters witness in Guatemala City said people were returning to work after evacuations which filled the streets with office workers calling friends and relatives on their cellphones.
"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 750 miles (1,000 km) away in Mexico City, where some office workers were also briefly evacuated.
Mayor 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.
(With reporting by Nelson Renteria in San Salvador; Writing by Krista Hughes; Editing by Simon Gardner and Vicki Allen)