A giant wall of dust has swept through the US city of Phoenix, Arizona, turning the sky brown, endangering drivers and delaying flights.

The dust storm, also known as a haboob, formed in Pinal County and headed north east for Phoenix.

The dust wall was about 3,000ft high and created winds of 25 to 30mph with gusts of up to 40mph said Austin Jamison, a meteorologist with the National Weather Service. Visibility was down to less than a quarter of a mile in some areas, he said.

"You have suddenly very poor visibilities that come on with all the dense dust in the air," he said. "With poor visibilities, that makes for dangerous driving conditions and that's arguably the biggest impact."

There were no immediate reports of accidents on roadways because of the storm, and the Arizona Department of Public Safety did not immediately return a request for information about road conditions.

Some departing flights at Phoenix Sky Harbour International Airport were delayed because of the storm, said airport spokeswoman Julie Rodriguez. Incoming flights from nearby cities including Los Angeles were being held until the storm cleared, she said.

Another giant dust storm in Arizona caught worldwide attention on July 5. That storm brought a mile-high wall of dust that halted airline flights, knocked out power for hundreds of people and turned swimming pools into mud pits.

Mr Jamison said Tuesday's storm was not as powerful or as large and would probably not last as long. "It's kind of like a ripple in a pond where it spreads out, slows down and fades out," he said.

Weather experts say haboobs only happen in Arizona, the Sahara desert and parts of the Middle East because of dry conditions and large amounts of sand. Pollution levels skyrocket during dust storms and create even more breathing problems for people with asthma and other similar conditions.

The dust also brings increases in a disease known as Valley Fever, a fungal pneumonia. Valley Fever thrives in the hot and arid south west in dirt found just a few feet beneath the earth's surface. It can be stirred up by construction, wind and other activity.