At least 16 people were killed when a passenger bus crashed on Indonesia’s main island of Java shortly after midnight on Monday, officials said.

The bus, which was carrying 34 passengers, went out of control on a toll road, slammed into a concrete divider and then overturned, according to Budiono, head of a search and rescue agency.

The interprovincial bus was en route from Jakarta to the historic city of Yogyakarta when it overturned while negotiating a curved exit ramp on the Krapyak toll road in Semarang, Central Java.

Budiono said the strong impact flung several passengers from their seats and trapped others inside the wreckage.

Police and rescue workers reached the scene around 40 minutes later and found six passengers dead on the spot. Ten more victims later died while being taken to hospital or during treatment.

A total of 18 injured passengers were admitted to two nearby hospitals, including five in critical condition and 13 in serious condition, Budiono added.

Television footage showed the yellow bus lying on its side as personnel from the National Search and Rescue Agency, police officers and bystanders gathered at the scene, while ambulances carried away the injured and the deceased.

Central Java Police Chief Ribut Hari Wibowo said witnesses reported the bus was speeding before the driver lost control. Speaking at Dr Karyadi General Hospital in Semarang, where the bodies were being identified, he said the driver was a replacement who suffered serious injuries but remained able to speak.

Police are still investigating the cause of the accident and questioning the injured substitute driver, Wibowo said, adding that tests would be conducted to check for the presence of banned substances, including drugs.