The corresponding decree was signed by President Cristina Kirchner.
According to recent reports, over 48 died in floods in La Plata, another 6 people were killed in inclement weather in the capital.
In the affected areas, which witnessed over 400 millimeters of precipitation in 24 hours, army units have been called in to extend aid to the population; distribution of drinking water and hot meals is underway.
Authorities have announced soft loans for housing reconstruction.
Security has been reinforced by riot police and the military.
The death toll from floods in the Argentine city of La Plata has reached 46 people. On Tuesday La Plata witnessed 30 inches of precipitation in practically three hours, causing half the city to be flooded. Dozens of people are still awaiting rescue on rooftops and in cars.
One of the city’s supermarkets was looted; spontaneous protests erupt in some districts. The Head of State Cristina Fernandez de Kirchner held an emergency meeting with the authorities of Buenos Aires province.
Due to the situation in La Plata, classes have been cancelled in schools, and Wednesday declared a holiday.
On Tuesday, heavy rains were registered in the Argentine capital and its suburbs. Downpours led to flooding, which killed six people.
At least 25 people died in flooding in the city of La Plata triggered by torrential rain in the region, an official said Wednesday.
The storm hit late Tuesday in the city of La Plata, capital of Buenos Aires province, and as the waters receded bodies started showing up, said governor Daniel Scioli.
Mr Scioli said city authorities had been discovering the bodies as the flood waters slowly receded.
At least another six people died in the city of Buenos Aires, where the rains lasted for seven hours. Many of them were trapped in their cars by rising flood waters and drowned.
Poor drainage meant that hundreds of thousands of residents woke up to flooded streets and power cuts.
One of those who died was a worker for the city's underground system who was electrocuted while trying to pump water from a flooded station.
Buenos Aires Mayor Mauricio Macri said about 350,000 people had been affected by the torrents of rain.
Thousands of cars were carried away by floods and hundreds of families had to be evacuated from their homes.
The city authorities said it was the heaviest April rainfall in a century.
The death toll from torrential rains in Buenos Aires has climbed to eight, most of them elderly people who either drowned or suffered heart attacks.
According to local meteorologists the Argentine capital has had a record 180 mm and more of rainfall over the past 24 hours.
Voice of Russia, AFP, AP, RIA, BBC