The cleaner who worked at the Grand Chancellor hotel developed systems on Wednesday and was tested the same day, returning a positive result later that night.
Health officials conducted contact tracing overnight.
"We need to ensure that there is no community spread, so we need to make sure that people in Brisbane are getting tested if they have systems," Premier Annastacia Palaszczuk said.
People living in Sunnybank Hills, Algester, and Calamvale in the south of Brisbane are being urged to get tested.
"We need the community to stay alert," she said.
The premier also announced that travellers from Greater Sydney had been banned from coming to Queensland, and Victoria may be next.
Chief Health Officer Jannette Young said she was eager to contain the virus spread as soon as possible.
"I want to find these cases right at the start of an outbreak, not down the track," Young said. "If we can find them now, today, then we can stop the outbreak spreading, and we don't need to put any restrictions in place."
Train from Altandi station to Roma street - Saturday 2 January at 7:00 amTrain from Central Station to Altandi station - Saturday 2 January at 4:00 pmWoolworths Calamvale North - Sunday 3 January from 11:00 am to 12:00 pmColes Sunnybank Hills - Tuesday 5 January from 7:30 am to 8:00 amNewsagent at Sunnybank Hills Shopping Town - Tuesday 5 January from 8:00 am to 8:15 am
Young said they are working with Queensland Transport to get GoCard information, but in the meantime urged people who boarded those trains to get tested if they show symptoms.
Currently there are 20 active cases of COVID-19 in Queensland.