Torrential rainfall submerged streets and cut off electricity in parts of Saudi Arabia's second largest city Jeddah, raising fears of a repeat of floods in 2009 which killed more than 120 people.

The last floods triggered a rare public debate about weaknesses in infrastructure in the top oil exporter, one of the world's richest countries.

On Wednesday, cars floated in streets turned into rivers, while putrid odours filled the air as sewage from underground tanks overflowed and mixed with flood water in the Red Sea port of four million inhabitants.   

Boats and helicopters searched flooded areas and residents said many people were unable to leave schools and workplaces.   

King Abdullah, who is resting in Morocco after back operations in New York, ordered rescue operations to be stepped up, warning "anyone who may delay this order", state media said.

"The order is to be implemented now without delay, to provide aid to minimise this damage, especially since the rain is expected to continue for days," the king said in a decree.

Authorities urged residents to stay indoors but gave no immediate assessment of damage or casualties. A spokesman for the civil defence did not return repeated calls for comment.   

"We are flooded. It's bad. The whole first floor of my house is filled with water and one of my couches is floating in the living room," said one woman in Jeddah.

"Why weren't we warned about this? There are helicopters rescuing people and cars floating in the streets," she said. - Reuters