Health authorities are worried about dengue fever outbreaks in two north Queensland towns and are trying to stop them spreading.

Thirty-five cases of dengue fever have been confirmed in north Queensland, with health authorities investigating another seven probable cases.

Public health physician Stephen Donohue said 18 cases were from inner-residential areas in Charters Towers, while the other 17 were from Townsville.

“This is a worrying and very unusual trend for this time of year,” Dr Donohue said.

He urged residents in affected areas to rid their properties of stagnant water to prevent the insects breeding, and urged them to spray dark areas where they like to inhabit.

“We really need the community to help stop this outbreak from worsening,” he said.