The Bruce Highway was cut by rising floodwaters in south-east Queensland on Saturday.
The ABC reports the highway was closed south of Gympie and the D'aguilar Highway has also been cut at Kilcoy.
The Mary River was expected to peak at 16 metres in Gympie on Sunday morning. Businesses there have been evacuated.
The ABC reports extra emergency crews have been sent to the city as a precaution.
The main rail line through south-east Queensland was also cut in many places by flooding.