The four victims drowned when an ambulance they were travelling in slid off a flooded road and into a canal, authorities told Reuters.
Rafael Correa, the Ecuador president, has ordered the army to help thousands of evacuees and extended an emergency decree in a bid to deliver about $21m in funds to affected areas.
In the the coastal city of Babahoyo, about 200 km southeast of the capital, Quito, cattle ranchers tried to move their herds to higher ground.
"The water came down here and last night the cows had water up to their necks. They couldn't walk," rancher Mauricio Quintanilla told Reuters news agency.