In all, 31 people are being tested for the virus, but none is considered to have had high-exposure risk.
All horses on affected properties are being monitored daily.
Two more rounds of testing for Hendra virus must be conducted before the quarantine can be lifted.
Biosecurity Queensland has meanwhile reminded horse owners that there are no general restrictions on horse movements in Queensland.
Queensland chief veterinary officer Dr Rick Symons said the agency had received several inquiries from concerned horse owners wanting to know about moving horses to and from events.
"With a number of horse-related events this weekend, including polo matches, horse jumping and races, it is understandable that people are seeking information.
"Hendra virus is not highly infectious and, consequently, the horse industry is not subject to movement restrictions for Hendra virus - except for the nine properties currently under quarantine."
But he added that horse owners needed to take precautions on their properties to protect their horses from Hendra virus infection.
They are urged to remove horse feed and water containers from under trees and, if possible, place them under a shelter.
Horses should also be removed from paddocks where flowering/fruiting trees are attracting flying fox bats and return horses only after the trees have stopped flowering/fruiting and the bats have left.
"Consider fencing off access to trees that are identified as attractive to flying foxes," Symons said.
Although current cases were all located in the south-east region, horse owners across the state should be vigilant for signs consistent with Hendra virus infection.
"While people are free to move their horses, we would encourage them to practice good biosecurity practices and not travel, work on or take unwell horses to other properties or equestrian events."