At least five have been killed including two children after a massive 8.1 earthquake struck off the south coast of Mexico triggering a tsunami.

The earthquake was felt across Mexico, toppling houses and shaking buildings in the country's capital amid reports tremors were detected as a far away as Austin, Texas - more than 1,300 miles from the epicentre.

A tsunami has already been detected in Mexico after the quake struck at 11.49pm last night, 76 miles southwest of the town of Pijijiapan, at a depth of 43 miles.

Terrified residents in Mexico City ran out into the streets after the quake struck, witnesses said. Tremors were stronger than a devastating earthquake in 1985 that hit the capital flattening swathes of the city and killing thousands. 

The US Tsunami Warning System said widespread hazardous tsunami waves were possible within the next three hours on the Pacific coasts of several central American countries - Mexico, Guatemala, El Salvador, Costa Rica, Nicaragua, Panama, Ecuador and Honduras. 

As far as 8700 miles away in the Philippines, the national disaster agency put the country's entire eastern seaboard on alert. Another tsunami warning centre said a tsunami had already developed in Mexico, with the largest wave measured at 2.3ft. 

The death toll has already risen to at least five people, including two children in Tabasco state.

Tabasco Gov. Arturo Nunez said that one of the children died when a wall collapsed, and the other was a baby who died in a children's hospital that lost electricity, cutting off the supply to the infant's ventilator.

The other three deaths were in Chiapas state, in San Cristobal de las Casas.

Elsewhere, terrified residents fled into the streets amid chaotic scenes in the wake of the huge tremor. 

'The house moved like chewing gum and the light and internet went out momentarily,' said Rodrigo Soberanes, who lives near San Cristobal de las Casas in Chiapas, a poor, largely indigenous state popular with tourists.

Chiapas Gov. Manuel Velasco told television station Televisa the roofs of homes and a shopping centre had collapsed in San Cristobal.