The spill, believed caused when a landslide ruptured a major oil pipeline, has turned waters black in a section of the Esmeraldas River, in the province of the same name.

The Emergency Operations Committee in the provincial capital, also called Esmeraldas, declared the environmental emergency.

Vilko Villacis, mayor of the city of more than 200,000 inhabitants, said the leak had caused "unprecedented" damages. His office halted the diversion of river water to an aqueduct supplying the city, and urged citizens to ration water.

On Friday, state-owned Petroecuador said it was working to address the emergency at the pipeline, part of the Trans-Ecuadoran Pipeline System (SOTE) which transports crude oil from the Amazon.

The company has not estimated the volume of oil spilled.

Ecuador last year produced 475,000 barrels of crude a day, exporting 72 percent of the total.

The SOTE is the most used pipeline system in the country, with the capacity to transport 360,000 barrels per day on the 500-kilometer (310-mile) journey from the Amazon to the Pacific coast.