The explosion rocked the popular eatery on the city's tourist-friendly waterfront about 7:30 p.m. local time, the height of the dinnertime rush.
A group calling themselves Muslims Against Global Oppression has taken credit for the attack, saying it was in retaliation for last week's missile attacks by the U.S. against suspected terrorist sites in Sudan and Afghanistan. But police have not confirmed the organization's involvement or motive.
According to Reuters, the explosive may have been tossed into the franchise from the street.
No damage was visible from the outside.
A police official tells Associated Press that one woman died and as many as 30 others were injured in the blast. No details on the victims have been released.
Founded by action heroes Arnold Schwarzenegger, Sylvester Stallone and Bruce Willis, and supported by their celeb pals, Planet Hollywood has nearly 80 outlets around planet Earth. The chain posted a multimillion dollar deficit last year.