UPDATE: A Maryborough fire inspector has said the "toxic smell" coming from a toilet block near the Town Hall was likely caused by works going on in the area.

Acting Inspector for Maryborough Command Jason McCloskey said two people were assessed for irritation of the throat caused by a strong chemical odour in the bathroom.

He said the smell was likely caused by fumes from cleaning products being pushed up through the pipework.

Act Insp McCloskey said crews would likely be on scene for up to three hours as investigations continued.

He said the large crowds gathered for Maryborough market day could present a challenge as crews worked to keep people from walking through the scene.

EARLIER, 11AM: EMERGENCY crews are on scene investigating reports of a "strong chemical odour" coming from a Maryborough toilet block.

A Queensland Fire and Emergency Service spokeswoman said four crews were on scene on the corner of Kent St and Lennox St, after getting the call just after 10am.

The spokeswoman said crews were sent in to test the air in the toilet block, and confirmed there was no fire.

Scientific investigators are on scene testing the air as well.

A Queensland Police spokeswoman said the Town Hall and toilet blocks had to be closed about 10.30am as crews investigated.

Emergency crews are investigating a strong odour coming from a Maryborough toilet block.
Emergency crews are investigating a strong odour coming from a Maryborough toilet block. Carlie Walker

A large area around the scene has been cordoned off as investigations continue.

A Queensland Ambulance Service spokeswoman said two patients were assessed on the scene but neither required transport to hospital.

More information to come.