A billowing wall of dust engulfed downtown Phoenix on Thursday, cutting visibility to a few hundred yards and delaying flights at the international airport, authorities and news reports said.

Driving rains and winds gusting at nearly 60 miles per hour also buffeted San Tan Valley, southeast of Phoenix in the early evening, according to the National Weather Service.

Roaring gusts downed trees and power lines in Pinal County, trapping drivers in their cars and preventing commuters from reaching their homes south of the state capital.

This storm hit during a very busy time for traffic, bringing down power lines over several miles on top of cars with visibility near zero, Pinal County Sheriff's Office spokesman Elias Johnson said in a statement.

Deputies will keep residents out until we can determine their safety is no longer at risk, he added.

The dust storm prevented planes from taking off or landing at Phoenix Sky Harbor International Airport for about 40 minutes, The Arizona Republic newspaper reported.

A call to the airport seeking confirmation of the delays was not immediately returned on Thursday.

In early July, a huge sand storm -- dubbed a haboob -- swallowed the Phoenix valley, darkening the streets, sending residents scrambling for cover and cutting power to thousands of homes.

Weather experts say haboobs frequently occur during the swelteringly hot summer monsoon season in the southwest United States.

(Reporting by  Tim Gaynor; Editing by Cynthia Johnston)