PORTOVIEJO/PEDERNALES, Ecuador, April 18 (Reuters) - The death toll rose to 350 on Monday from a devastating earthquake that hit Ecuador at the weekend, as rescuers hunted for survivors, victims clamored for aid and looting broke out in the Andean nation's shattered coastal region.

More than 2,000 people were injured in Saturday night's 7.8 magnitude quake, which ripped apart buildings and roads and knocked out power along the Pacific coastline.

President Rafael Correa, giving the new tally of fatalities from the town of Portoviejo inside the disaster zone, told Reuters the number of dead had risen to 350 but feared that would rise further.

"Reconstruction will cost billions of dollars," said Correa, as survivors begged him for water, adding later on Monday the impact on economic growth "could be huge."

The normally upbeat socialist president looked deeply moved as he chatted with victims during a tour of the destroyed town in the South American OPEC nation, which was already suffering from the global slump in crude oil prices.

One U.S. citizen is confirmed to have died in the quake, the State Department said on Monday, and Britain's Guardian newspaper said Sister Clare Theresa Crockett, 33, a missionary nun from Derry in Northern Ireland, also died.