A search and rescue operation has been launched in Ingham inundated the town, completely cutting off the community.
Police said the man was last seen entering floodwaters about 5.15pm on Tuesday.
"The man ... remains unaccounted for, despite water and aerial searches this morning," a police statement said.
He is described as Caucasian, about 188cm tall, with dark hair.
He was wearing black shorts, a black singlet, a black backpack and arrived on a blue bicycle.
Anyone with information should contact police but residents have been urged to avoid the area.
Ingham has been one of the worst hit by heavy rainfall that has forced hundreds to evacuate across north Queensland, with two lives lost in floodwaters.
The community is still reeling after an elderly woman's body was found in a cane field on Tuesday.
The 82-year-old became the second flood-related fatality after days of downpours.
A persistent deluge is hitting rain-soaked northern Queensland, with Ingham hit hard. (HANDOUT/ERGON ENERGY)
The Ingham community had already been rocked after a 63-year-old woman died when an SES boat helping people through floodwaters struck a tree and flipped on Sunday.
Power has been cut, food supplies are dwindling and telecommunications also affected due to what has been described as a "one in 100 year" flood.
Floodwaters devastated the region after the nearby Herbert River rose beyond a 15.2m flood record set almost 60 years ago, with residents told on Wednesday they had no more running water.
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