MANILA, Philippines - (2nd UPDATE) A tour bus fell off a cliff on Sunday morning in Barangay Cansumuruy in Balamban, Cebu.

The fatalities have risen to 20 in the evening, with the remaining 30 victims injured. It is uncertain how many more victims are being rescued or how many more bodies rescuers are trying to retrieve.

Initial reports showed that the victims, all Iranian nationals, were medical students who were on their way to a picnic when the bus carrying them lost control and fell off a steep cliff along the Transcentral Highway.

That portion of the road is said to be prone to accidents.

"Apparently, the bus brakes malfunctioned. The highway connecting Cebu and Balamban is like Kennon road in Baguio -- they were downside when the driver realized that [the bus brakes are] no longer functioning. So they hit an electric post, then tilted to the side and fell into the ravine," said Lani O'Neres, regional police director of Cebu district 7, in an interview on ANC's "Prime News" on Sunday night.

"We want to lift the bus but it might not be good now...So we retrieve [the victims] first then the bus," he added.

Efforts are underway to confer with Iranian officials on the fate of their nationals.

Meanwhile, the road remains open to motorists as the military undertakes efforts to prevent more accidents.