One person has died and at least 20 others have been injured in a tourist bus roll over in Western Australia’s south-west, police say.

The bus carrying about 50 tourists rolled onto its side on a rural highway near Weld River, 65km south of Manjimup on Wednesday morning.

Sergeant Greg Lambert said 20 people were injured, 10 of whom were in a serious condition.

“We have 20 persons who are injured, of those ten are considered serious, and at this stage it’s still … one person deceased,” Sgt Lambert said.

He said the exact location of the crash was 5km south of Martin Road on the South West Highway, which is 76km south of Manjimup.

A rescue helicopter and five ambulances have been dispatched to the scene.

Sgt Lambert said he understood it was a single-vehicle accident on a rural highway.

The nationalities of the people on board the bus were not yet known, but Sgt Lambert said it was believed most of them were elderly.

The South West Highway had been closed in both directions from Walpole to Manjimup until at least 3.30pm (WDT), a police spokeswoman said.

One lane of the highway would be reopened after police and emergency services had cleared the scene of the accident.

The Royal Flying Doctor Service (RFDS) has sent a third plane to the scene to help with the injured.

“We will obviously bring them back as quickly as we can, but at the moment all of the patients are in Manjimup Hospital,” RFDS spokeswoman Lesleigh Green told the Fairfax Radio Network.

“Our medical teams … have gone in to the hospital to assist because apparently there is a shortage of doctors and nursing staff.

“They’re in there basically helping to triage patients and making a decision about who needs to come back quickly.

“We do know that there are stretcher patients, which means they are fairly seriously injured and they will need to come back via RFDS – two patients to each aircraft.”

Shire of Manjimup councillor and volunteer ambulance officer Paul Owens said the bus was carrying a group from a RSL club in Perth.

“It was pretty messy … there’s a fairly long line of people sitting on the side of the road with various injuries from unconscious to broken limbs and major lacerations, and there was probably about five or six people still trapped inside the bus,” Mr Owens said from the Manjimup District Hospital.

“It was off the highway on its side and we retrieved most casualties out through the front window.

“We cut a hole in the back of the bus there and also there’s an emergency exit in the roof which we took them out the side of as well.”