Queensland Health is investigating the cause of a mysterious illness that has gripped staff at the Queensland Fire and Rescue Service (QFRS) training facility in Brisbane's east.

The Service has temporarily closed its training facility at Whyte Island, near Lytton, after 41 people fell ill today.

Emergency Services Minister Neil Roberts says the incident is significant given that around a third of the 149 people who were at the site yesterday are unwell.

"At this stage people are just reporting headaches and nausea and as I've indicated vomiting and diarrhoea so it's still, it's very uncomfortable for them," he said.

"So that's why we've engaged the public health unit of Queensland Health to assist us in trying to get to the bottom of what might have caused the bouts of illness."