SECURITY was tight yesterday as hundreds of Scientologists and their guests gathered to open the controversial church's new headquarters in Ascot Vale.

All afternoon a procession of well-dressed church members could be seen making their way to the Mt Alexander Rd site, which was guarded by about 20 security guards.

High-profile Scientologist Kate Ceberano arrived about 4.30pm.

The massive compound, which was bought from the Catholic Church for $7 million in 2005, has been renovated at an estimated cost of $20 million, and includes a large chapel, a public auditorium, course rooms and a multimedia public information centre.

Guests - including Lord Mayor Robert Doyle - arriving for the opening were greeted by a small number of protesters wearing masks and chanting anti-Scientology slogans.

"I am here because my friend Kate Ceberano invited me to be here and people should take nothing more from it than that," Mr Doyle said.

But he was attacked by independent South Australian Senator Nick Xenophon.

"He is the Lord Mayor of Melbourne and indirectly he is lending his support to this organisation," he said.