At least 52 people have drowned in their homes and cars, or were electrocuted as floods swamped Buenos Aires.
Thousands have been evacuated from their homes At least 46 died on Wednesday in and around the city of La Plata. Six deaths were reported a day earlier in Argentina's capital.
Many people climbed onto their roofs in the pouring rain after storm sewers flooded forcing water into houses.
"It started to rain really hard in the evening, and began to flood," Augustina Garcia Orsi, a 25-year-old student, said.
"I panicked. In two seconds I was up to my knees in water. It came up through the drains - I couldn't do anything."
Many claim officials have not done enough The rains also flooded the country's largest oil refinery, causing a fire that took hours to put out.
The La Plata refinery suspended operations as a result, and Argentina's YPF oil company said an emergency team was evaluating how to get it restarted.
"Such intense rain in so little time has left many people trapped in their cars, in the streets, in some cases electrocuted," Governor Daniel Scioli said.
"We are giving priority to rescuing people who have been stuck in trees or on the roofs of their homes."
The region of Buenos Aires has been worst affected President Cristina Fernandez visited Tolosa, a La Plata neighbourhood where she grew up and where her mother was among those evacuated.
She announced security measures to combat vandalism, help for identifying the dead, and three days of national mourning for the victims.
At least 2,500 people were evacuated from their homes to about 20 centres in the La Plata area, which is about 37 miles (60km) southeast of Argentina's capital.
The rains are expected to ease later The flooding threatened to ruin food supplies across La Plata's metropolitan area, which has nearly one million people.
National Planning Minister Julio de Vido estimated that 280,000 people remain without power across the city and surrounding province of Buenos Aires, where most Argentines live.
"Our job is focused on restoring service, but we're going to wait until the equipment dries to guarantee the safety of the electricity workers, because we don't want any deaths," he said.
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