A Saudi lawyer said yesterday he will sue the city of Jeddah, as thousands took to Facebook to blast authorities in a rare burst of open outrage after floods killed almost 100 people in the Red Sea port.

The toll jumped to 98 from last Wednesday's floods, after authorities discovered more bodies, said a civil defence official.

Human rights lawyer Walid Abu al-Kheir said families of victims of the disaster were supporting the lawsuit, which will allege massive mismanagement of city works construction by the Jeddah government as a key cause for the flooding.

"They didn't make the drainage work. They have told us for three years or more that it has been completed," he said. "Even people from the city government said there were mistakes."

A huge rainstorm sparked flash floods in the Red Sea port city, with many victims caught in their cars and drowning in two metres or more of water.

Roads were destroyed and cars and trucks left in piles after the waters receded last Thursday.

Electricity is still out in some of the worst hit parts of the city, the country's second largest after Riyadh.

With public protests banned in Saudi Arabia, Jeddah residents have taken to the internet to attack the government.

More than 11,000 people joined a Facebook page created three days ago to complain about the floods, saying the city government and contractors were at fault for not building adequate infrastructure.