Heavy rains in the Saudi coastal city of Jeddah on Thursday delayed flights, forced school suspensions and closed the road to Makkah, Islam's holiest city, state media reported.

Jeddah, a city of roughly four million people positioned on the Red Sea, is often referred to as the "gateway to Makkah", where millions perform the Hajj and Umrah pilgrimages each year.

Images posted to social media on Thursday showed standing water snarling traffic in Jeddah and partially submerging some vehicles.

The city's King Abdulaziz International Airport said that "due to weather conditions, the departure of some flights has been delayed" and urged passengers to contact carriers for up-to-date schedules.

The official Saudi Press Agency reported before dawn that schools in the city would be suspended as rains were forecast to continue throughout the day.

Schools were also closed in the nearby towns of Rabigh and Khulais "to preserve the safety of male and female students", SPA said.

The kingdom is in the middle of final exams, yet schools had already been closed nationwide on Wednesday after King Salman declared a holiday following Saudi Arabia's shock defeat of Argentina in the World Cup.

Winter rainstorms and flooding occur almost every year in Jeddah, where residents have long decried poor infrastructure.

Floods killed 123 people in the city in 2009 and 10 more two years later.