Dry and gusty thunderstorms with the risk of lightning strikes sparking new fires are forecast to tear through the Darling Downs late this afternoon.

Fire authorities have warned that wind gusts of up to 100 kilometres per hour are set to fan existing fires.

But the real danger is from high-voltage lightning strikes, which could set tinder-dry grazing land alight and create new spot fires.

Queensland Fire and Emergency Services (QFES) Acting Chief Superintendent Kevin Reading said they were expecting new fires to be started by the storms "because of how dry the ground is".

"As the lightning strikes, the electricity has an element of heat to it so that heat could catch a piece of dry grass that has no moisture in it," he said.

"That starts small obviously, but as the wind increases you have got the fuel, you have got the oxygen and the ignition source — so that is what can start a fire."

QFES Assistant Commissioner John Bolger said crews were "well set up" for the expected dangerous conditions.

Read more: https://www.abc.net.au/news/2019-09-17/queensland-bushfire-dry-storm-lightning/11517754