The track - which features an appearance from rapper Snoop Dogg - is also top of the UK, US and Irish singles charts at present.
B.o.B. and Hayley Williams hold steady at two with 'Airplanes', while US country star Uncle Kracker zooms from 15 to three with 'Smile'.
Meanwhile, Enrique Iglesias's 'I Like It' climbs from eight to five - the Spanish singer's best position Down Under since he reached the summit with 'Hero' in 2001.
Eminem and Rihanna's 'Love The Way You Lie' becomes the only new track in the top ten this week after jumping from 14 to eight.
The top ten singles in full (click where possible for our reviews):
1. (1) Katy Perry ft. Snoop Dogg: 'California Gurls'
2. (2) B.o.B. ft. Hayley Williams: 'Airplanes'
3. (15) Uncle Kracker: 'Smile'
4. (3) Usher ft. will.i.am: 'OMG'
5. (8) Enrique Iglesias ft. Pitbull: 'I Like It'
6. (6) Travie McCoy ft. Bruno Mars: 'Billionaire'
7. (4) Eminem: 'Not Afraid'
8. (14) Eminem ft. Rihanna: 'Love The Way You Lie'
9. (5) Yolanda Be Cool & DCup: 'We Speak No Americano'
10. (7) David Guetta & Chris Willis ft. Fergie & LMFAO: 'Gettin' Over You'