The death toll from Ecuador's earthquake was set to rise sharply after authorities warned that 1,700 people were still missing and anger gripped families of victims trapped in the rubble.

Three days after the powerful 7.8-magnitude quake struck Ecuador's Pacific coast in a zone popular with tourists, 480 people are known to have died, the government said Tuesday.

Sniffer dogs and mechanical diggers were busy at work in the wreckage of coastal towns such as Pedernales and Manta as the stench of rotting bodies grew stronger under the baking sun.

International rescuers and aid groups rushed to help victims as searchers dug for families trapped in the debris of homes, hotels and businesses.

"We have 2,000 people listed that are being looked for, but we have so far found 300," Deputy Interior Minister Diego Fuentes told reporters in the capital Quito.

Some 4,605 people were injured, according to the latest government figures.

In a glimmer of good news as he toured the affected areas, President Rafael Correa said that 54 people had been rescued alive from the rubble.

Still, hope of finding more victims alive was fading fast as the crucial three-day mark was reached late Tuesday. 

Locals in devastated towns such as Manta -- population 253,000 -- started to lose patience.

"The rescue has been very slow and precious lives have been lost. We relatives have been waiting here since Saturday night," said Pedro Merro, who said his cousin was under the wreckage of a three-floor market in Manta.

Luis Felipe Navarro said he was sure there were people alive in the concrete and twisted metal of a building he owned -- one of around 800 structures toppled in the quake.

"I have received messages on my telephone. They say there are 10 of them in a cavity," he said. "But the rescue teams will not listen to me."

 US pledge

 "It is very hard but we are moving forward," Correa told AFP in Manta, where he handed out food and water in what resembled a war zone.

Hundreds of emergency workers from Colombia, Mexico, El Salvador, Spain and other countries were helping overwhelmed Ecuadorian officials.

Fears rose for thousands of people left homeless by the quake, prey to disease-bearing mosquitoes and dirty drinking water.

Firefighting captain Freddy Arca pointed to the ruins of a hotel in Manta as drills and jackhammers rattled around him.

"We know that there is a man, his wife and their two-month-old baby in there. And there may be up to nine other people," he said.

UNICEF warned that 150,000 children were affected by the disaster.

It said landslides were complicating rescue efforts in some areas, and some towns were without electricity.

The Spanish Red Cross estimated that up to 100,000 people would need assistance.

In Pedernales, some 180 kilometers north of Manta, a football pitch was serving as a makeshift morgue, medical center and distribution center.

But not everyone was able to get help.

"We came here to ask for food but they've already handed out the supplies," Gema Guillen, a mother of three, told AFP.

The family had lost their home in the quake and was now sleeping on the floor, she said.

US President Barack Obama called Correa Tuesday and told him the United States would do "all it can to support Ecuador's recovery," the White House said in a statement.

Ecuador's government said it had access to $600 million in emergency credit overall, but Correa said rebuilding will cost up to $3 billion and could take two or three years.

It was Ecuador's worst quake in nearly 40 years.

 Noises in the rubble

 In Manta, two young women with eyes red from crying wandered around near the ruined hotel on Tuesday.

"My brother Irvin is under there," said one, Samantha Herrera, 27. "The firefighters only arrived this morning. Ecuador is not prepared for such a catastrophe."

Rescuers said they could hear a noise from someone under the wreckage. Arca, the firefighting captain, ordered the skinniest members of his team to wriggle into a gap in the rubble.

The man came back up looking pale. Searching for survivors, he found two dead bodies.

"But we can still hear the noise," Arca said.