A bus carrying Dutch tourists has crashed in southern Portugal, killing three of the tourists and injuring 30 others and the Portuguese bus driver.

The bus went off a highway on Wednesday night and rolled over into a gully, emergency team leader Vitor Vaz Pinto said.

The bus was carrying 33 Dutch tourists who had arrived at Faro airport in Portugal's Algarve region, one of Europe's most popular vacation destinations, he said.

He told reporters that authorities had spoken to the driver but he declined to speculate on the possible cause of the crash, which is under investigation.

The Dutch ambassador in Lisbon was heading to the Algarve and Foreign Ministry staff from The Hague also were flying to Portugal to help families of victims, Dutch Foreign Ministry spokeswoman Ilona de Ruyter said.

Mr Vaz Pinto said 156 rescue workers, 101 emergency vehicles and two helicopters attended the scene of the crash which happened at around 11pm local time.