At least 12 people were killed, including four students, when a public bus carrying school pupils and a truck loaded with rocks and soil collided in mountainous western Slovakia on Wednesday, rescuers and officials said.

Officials said some 17 people were hurt in the crash, which happened on the outskirts of the city of Nitra, a regional capital some 80 kilometres (50 miles) east of Bratislava, around 1pm local time.

Images from the site showed the truck lying on its side and the bus wedged in a ditch, with a large amount of soil and rocks strewn on the road.

"Mostly teenagers, secondary grammar students, were aboard this regular bus line from Nitra to Jelenec," Nitra fire brigade spokesman Michal Varga told AFP, adding that the truck was "fully loaded with rocks". 

He added that the causes of the crash were unknown.

The fire and rescue department said on its Facebook page that the toll was 12 dead and 17 injured.

Minister of Health Andrea Kalavska told journalists at the accident site that of those killed, "at least four were underage".

Interior Minister Denisa Sakova told the press at the site that the truck was "probably overloaded".

According to reports on Slovak commercial TV channel Markiza, the truck skidded and hit the bus from the side. 

The bus serves as a regular line between Nitra and the village of Jelenec east of the city.

Rescuers at first put the number of dead at 13, with 20 injured, before correcting the toll.

Some 30 firefighters are at the scene to help the injured, while rescuers have deployed helicopters and sent in psychologists.

They said rescue work was hampered by bad weather as Slovakia was hit by heavy rain on Wednesday, although there was no rain when the accident occurred.

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