Authorities now say the Cunningham Highway on Queensland's southern Darling Downs will remain closed at least until the weekend.

A 300-tonne boulder came down at Gap Creek Bridge near Warwick yesterday, blocking the highway in both directions.

Traffic is being diverted through Toowoomba and other local roads.

Paul Noonan from Transport and Main Roads says the massive rock has caused serious damage.

"When the rock's come down it's actually embedded itself about one-and-a-half-metres into the road surface," he said.

"What that means of course is that not only do we have to remove the rock by breaking it apart we also then have to repair the road surface.

"That'll take probably a couple of days."

Southern Downs Mayor Peter Blundell says it is frustrating.

"It's impacting on our tourism businesses, it's impacting again on our freight and transport network," he said.

"It's particularly important that road information is very up-to-date and very current and also those issues are resolved as quickly as possible."

Police say it is fortunate the massive rock fall did not hit a car. ( Supplied by Qld Police )

Transport Minister Scott Emerson says the boulder is nine metres long and five metres high.

"Unfortunately it did come down yesterday but it didn't endanger motorists," he said.

"No-one was put at risk but now the task is there to remove it from the road.

"It's not very common for them having to remove a massive boulder of this size."

Mr Emerson says work had been done in the area to prepare for the wet season.

"We've been working on that site," he said.

"There's about 800 tonnes of rock and debris that over the last week we have been working to remove, so we are doing work around that area.

"Unfortunately that boulder, which was unstable, has come loose and landed on the highway."