A fresh tremor rattled Ecuador overnight, a 6.1 magnitude jolt that was the strongest aftershock since a lethal earthquake killed hundreds of people on Saturday. 

The US Geological Survey said the tremor was centered offshore, 25kms (15 miles) west of Muisne, at 3:33am local time. The previous strongest aftershock was magnitude 5.7.

There were no immediate reports of further damage.

Ecuador's National Prosecutors Office says the death toll from Saturday's devastating earthquake has risen to 525, up from a previous official toll of 507.

This photo taken on April 19, 2016 shows residents working at a collapsed home after an earthquake struck off the Pacific coast, in Pedernales, Ecuador. Photo: Reuters

The office said on its official Twitter account today that there were at least 11 foreigners among the dead.

It said 15 of the dead remained unidentified but none was foreign.

The office said 435 of the dead were found in the Manta, Portoviejo and Pedernales areas.

The Defense Department reported Tuesday that more than 200 people were still missing following the 7.8-magnitude earthquake Saturday.

Thousands of people have been left homeless, making them vulnerable to dirty drinking water and disease.