39 deaths confirmed after a strong earthquake struck off the Pacific coast of Guatemala this morning.

The quake rocked the capital Guatemala City and shook buildings as far away as Mexico City and El Salvador. 

Many are believed to be still trapped under rubble near the Mexican border in two different mountain towns.

Landslides were blocking roads in some areas, authorities said, and about 40 houses were severely damaged.

It is believed to be the strongest quake to hit Guatemala since 1976.

Guatemala's President Otto Perez said that as many as 100 people were unaccounted for, based on reports from relatives.

The quake struck off Guatemala's Pacific coast, 24km south of Champerico and 163km west-southwest of the capital.

Evacuations in Guatemala City filled the streets with office workers calling friends and relatives on their mobile phones, but people soon returned to work.

The epicentre was 42km 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 1,232km away in Mexico City, where some people also fled offices and homes

The Pacific Tsunami Warning Center said a very small tsunami was registered on Guatemala's coast, adding there was a risk of localised damage within an 100km radius.