LOS ANGELES —  Several envelopes containing white powder were sent to the Church of Scientology in what appeared to be a hoax that prompted street closings and evacuations in Southern California, the FBI said Thursday.

The envelopes were mailed to at least 19 church addresses in Los Angeles and Orange counties, and began showing up Wednesday, the FBI said.

Glendale police shut down a street for two hours and Tustin authorities evacuated 60 people from buildings as hazardous materials teams were called in.

The FBI said initial tests indicated the powder was harmless but more tests were being conducted.

The church declined to comment Thursday.

The Los Angeles-based Church of Scientology was established in 1954 by science fiction writer L. Ron Hubbard and claims 10 million members around the world, including celebrity devotees such as Tom Cruise and John Travolta.