At least 40 people were killed and eight others injured after a passenger bus plunged into a deep ravine in Pakistan's southwestern Balochistan province on Friday, officials said.

According to police, the overcrowded bus was likely speeding. An investigation has been launched to determine the exact cause of the crash.

The bus was travelling from the southwestern city of Quetta when it lost control, veered off the road and fell into the ravine in Dana Sar, a remote mountainous area near the border of Balochistan and Khyber Pakhtunkhwa provinces, according to Shahid Rind, a spokesperson for the Balochistan government.

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The bus was carrying 48 passengers, including those who had transferred from another bus that had broken down, officials said.