ASUNCION/MONTEVIDO, Dec 26 (Reuters) - More than 100,000 people have had to evacuate from their homes in the bordering areas of Paraguay, Uruguay, Brazil and Argentina due to severe flooding in the wake of heavy summer rains brought on by El Niño, authorities reported on Saturday.

In the worse affected country, Paraguay, around 90,000 people in the area around the capital city Asuncion have been evacuated, the municipal Emergency Office said. Many are poor families living in precarious housing along the banks of the River Paraguay.

The Paraguayan government has declared a state of emergency in Asuncion and seven regions of the country to free up funds to help those affected.

In Alberdi, some 120 kilometers (75.5 miles) south of Asuncion, the government has recommended that 7,000 more families living along the banks of the River Paraguay evacuate.

More than 9,000 people in Uruguay also had to flee their homes, according to the national Emergency Office, which added that it expected water levels to remain at their current level for several days before subsiding.

“The flooding is caused by the El Niño weather phenomenon,” Uruguay Emergency Office Chief Fernando Traversa said. “We knew it would have its strongest impact towards the end of spring, start of summer ... but we could not know how much.”

This year’s “El Nino,” which sparks global climate extremes, is the worst in more than 15 years, the U.N. weather agency, the World Meteorological Organization (WMO), said last month.

“Severe droughts and devastating flooding being experienced throughout the tropics and sub-tropical zones bear the hallmarks of this El Nino, which is the strongest in more than 15 years,” WMO chief Michel Jarraud said in a statement.

In northern Argentina, around 20,000 people have had to abandon their homes, the government said on Saturday.

“We are going to have a few complicated months, the consequences will be serious,” said Ricardo Colombi, the governor of the Corrientes region, after flying over the worst affected areas with national Cabinet Chief Marcos Pena.

Pena said national government aid was already on its way and the new president, Mauricio Macri, who took office earlier this month, intended to make improving infrastructure a priority so that such flooding did not occur again.

“Argentina has a very big lack of infrastructure,” he said.

Brazil’s President Dilma Rousseff also flew over the flooded areas on the border with Argentina and Uruguay on Saturday morning. Rio Grande do Sul state Civil Defense said 1,795 people were left homeless there after 38 towns were affected by heavy rains. (Additional reporting by Sarah Marsh in Buenos Aires and Anthony Boadle in Brasilia; Writing by Sarah Marsh; Editing by Sandra Maler)