A 6.9-magnitude earthquake has struck about 170km (105 miles) south-east of Ecuador's capital, Quito
The quake happened at 0654 local time (1154 GMT), at a depth of about 190km, the US Geological Survey (USGS) said.
"Had it been less deep, it would have caused quite a lot of damage," said Sandro Vaca of Ecuador's geophysics institute.
No tsunami warnings were issued and there were no immediate reports of casualties or damage.
The strength was initially measured by the USGS at 6.7 then raised to 7.2 before being set at 6.9.
The earthquake was reportedly felt in Quito.
The USGS also said the quake was 140km east of Ambato and 160km south-south-west of Nueva Loja.
Maria Fernanda Fuentes, who works in a hotel in central Ambato, was driving at the time of the quake but told the BBC her co-workers at the hotel had said the tremor was "long and strong".
All the lamps had moved and several of the guests came down to the lobby looking worried, she was told.
No major damage has been reported in the city so far. The depth of the quake may have reduced its effects.