Las Vegas, Nevada -- Las Vegas police said it took about two hours to clear up a traffic mess caused by an electrical transformer explosion behind the Monte Carlo casino.

The blast and resulting fire created a cloud of smoke that shut down the northbound lanes of Interstate 15.

Metro Police told the Las Vegas Sun there were no injuries and Monte Carlo guests had to be evacuated.

The cause of the explosion, which occurred around 12:30 a.m. MDT, was not known.