Justin Bieber's trial on charges of driving under the influence, resisting arrest and driving with an expired licence has been delayed.

The pop star's trial was due to take place on May 5 but it has been moved to July 7 by a judge in South Florida.

Miami-Dade County Judge William Altfield granted a motion for a postponement sought by Justin's lawyers.

The star's attorney Roy Black said more time was needed to examine evidence and make decisions about how to proceed.

Justin, 20, was arrested on January 23 in Miami Beach after what police described as an illegal street drag race between the singer's rented Lamborghini and a Ferrari driven by RnB singer Khalil Amir Sharieff. Neither was charged with drag racing, but both were charged with driving under the influence. Justin was also charged with resisting arrest without violence and driving with an expired licence.

Both have pleaded not guilty, although Justin told police he had been smoking marijuana that night, according to a Miami Beach police report.

Alcohol breath tests found the Baby singer's level below the 0.02 limit for underage drivers. Urine tests showed the presence of marijuana and the anti-anxiety drug Xanax in his system, and a video of police sobriety tests showed Justin walking unsteadily.

Black said if the case proceeds to trial, he would likely challenge some of the tests and the results, although he would not go into any details.

"There are some serious matters regarding the testing," he said.

Black told Altfield that one reason for the case's slow pace is that all decisions must be made at the "executive suite" level in Justin's camp.

Most defendants in the singer's position eventually accept plea deals rather than going to trial, which could expose him to stiffer penalties including jail time. Black said it was premature to discuss which way Justin would go.

"Those decisions have not been made," he said.