The United Nations will distribute food to more than a quarter of a million people who survived Ecuador's devastating 7.8-magnitude earthquake but are growing hungry in its aftermath, the organization said on Monday.

The sweeping aid operation was being rolled out as the scale of the disaster was coming into sharper focus more than a week after the April 16 quake ravaged the country's Pacific coast.

About one in every 30 Ecuadorians, or half a million people, were in need of food assistance after the quake disrupted their livelihoods, the UN World Food Programme said in a statement.

WFP was gearing up to assist the 260,000 most needy among them, including children, people living in shelters and those hospitalized. The situation on the ground remained grim, WFP spokesman Alejandro Chicheri told the Thomson Reuters Foundation in a telephone interview.

The death toll in the small South American country passed 650 on Monday.

"There are a lot of people on roads asking for help," he said. "People are hoping to get assistance."

The emergency aid will build on efforts by the government and scores of foreign aid workers who are also distributing food, water and medicine in the quake zone.

WFP estimates the cost of its three-month operation at $34 million, a sum that will need to come from public and private donors, Chicheri said.

President Rafael Correa announced on Saturday eight days of national mourning for the victims of the quake.

He said last week the quake inflicted $2 billion to $3 billion of damage to the oil-dependent economy and could knock two to three percentage points off growth.

The April 16 earthquake was the worst the country has ever experienced in its history, the WFP said.