The China GT Championship has upgraded security for the upcoming race in Zhuhai after assessing the expected crowd size, the organizers of the car racing event sponsored by tech giant Xiaomi said today, dismissing online speculation that the move was due to celebrity participants. The event, which will kick off tomorrow, features Chinese actor Wang Yibo in the GT3 category and singer Zhou Yiran in the GTC category. Tickets were sold out within half an hour.