The death toll from floods devastating northern Chile has risen by one to at least 24, officials said Wednesday, as President Michelle Bachelet cancelled a trip to a regional summit to cope with the crisis.

Another 69 people, up by 12 from the last tally, remain missing, the National Emergency Office said.

The flash floods broke out last week in the normally arid north, home to the world's driest desert.

Entire towns have been submerged by water and thousands of people have been left homeless.

The number of dead found in thick mud left behind by the floodwaters has risen steadily as the clean-up continues.

"I'm convinced that more bodies will appear," the mayor of the town of Chanaral, Yerko Guerra, told local media earlier Wednesday.

Adding to those fears, the air force said a civilian helicopter had gone missing during emergency relief work in Atacama region. Media reports said it was carrying four passengers.

The floodwaters swept away entire towns and left tens of thousands of people without water or electricity.

With the region struggling to cope with the devastation, Bachelet announced she would stay home to oversee the disaster response rather than attend the Summit of the Americas in Panama on April 10 and 11.

Thirty-five leaders are invited to the summit, where US President Barack Obama and Cuba's Raul Castro will meet for the first time since announcing a historic rapprochement between their countries in December.

"Today marks one week since we were hit by the painful tragedy that lashed northern Chile," Bachelet said. "We still have a lot to do."

Some 7,000 soldiers and police have been deployed to help with the clean-up, clear roads and search for the missing.

On Thursday, 1,200 emergency housing units are due to arrive in the region.

Health officials have warned there is a high risk of outbreaks of gastrointestinal and respiratory diseases because of the mud and lack of drinking water.

The government has declared a health emergency for the zone and sent thousands of units of flu, tetanus and hepatitis A vaccines.