Two people have died after powerful waves up to 4 metres high pummelled the coasts of Ecuador and Peru, authorities said.
Ecuador's secretary for risk management, Jorge Carillo, described the incident as an "extreme event" and warned that more waves could be on the way.
"Unfortunately, we have two deaths," in Ecuador's south-western Manta region, he said.
In neighbouring Peru, the head of the naval Oceanographic Department, Enrique Varea, said almost all ports were closed because of the constant battering of waves.
He forecast that the waves "will continue in coming days," but expected them to calm somewhat and return to normal in the first days of January.
Larry Linch, head of the Civil Defense unit in Peru's Callao region, said climate change "is behind these sorts of anomalous waves".
Images on local media showed jetties and public squares submerged in some parts of Peru, sending residents fleeing to higher ground.
According to the Peruvian navy, winds along the ocean's surface are creating waves off the US coast.
Many beaches along the central and northern stretches of the country were closed to prevent risk to human life, authorities said.
Fisherman asks for more help
Many fishing boats were damaged, while those that were spared were still unable to work in the dangerous conditions.
"We need help from authorities. Here, we've lost some 100 boats," one fisherman told TV Peru.
"I'm 70 years old, and I've never seen such unusual and strong waves," he said.
Thirty-one fishermen stranded in the swell were rescued Saturday afternoon by the navy, while one told local radio that about 180 more remained at sea.
Many of them had struggled to bring their boats back to Acapulco beach in the Tumbes region.
In Canoas de Punta Sal, which is further south of Tumbes, local Mayor Javier Pazo speculated thousands of people were stranded.
"Over 2,000 fishermen in Canoas de Punta Sal are stuck."
Big waves were also seen crashing into the central Chilean coast in Vina del Mar, sparking warnings from authorities.
Callao, which sits adjacent to the capital Lima and is home to Peru's largest port, closed several beaches and barred tourist and fishing boats from venturing out.
"There is a major problem," La Cruz district Mayor Roberto Carrillo Zavala told AFP after surveying damage via helicopter with Peru's minister of defense, Walter Astudillo Chavez.
"The most affected have been the fishermen," Cr Zavala said.
"We hope nothing more happens, as this would significantly impact the economy."
The phenomenon began on Christmas day and will last until January 1, according to Peru's National Emergency Operations Center.
AFP/Reuters
