Massive grassfire threatening homes near Brisbane

A waterbombing helicopter has been brought in to battle a fast-moving out-of-control grassfire, threatening homes west of Brisbane.

A watch-and-act alert has been issued for residents near Grantham, with authorities warning people to be ready to activate their bushfire survival plan and be ready to evacuate.

The large fire was travelling from Phillips Road in Grantham and has now crossed the busy Warrego Highway around 100km from Brisbane. 

More than 14 fire crews are on scene battling the blaze.

Both lanes of the Warrego Highway remain closed to traffic with drivers urged to avoid the area.

Traffic was earlier gridlocked.