The death toll from a passenger bus carrying guests home from a wedding that plunged into a river in northern Pakistan has risen to at least 26 people, officials said, with the bride so far the only known survivor.

"The death toll has increased to 26 while one woman remained unhurt in the accident," Muhammad Zubair, a local police official of the Diamer district in northwestern Gilgit-Baltistan region, said over the phone.

Wazir Asad Ali, a rescue official in Gilgit-Baltistan, said the bride was out of danger and she was being treated at a hospital in Gilgit city.

Last evening, a bus carrying a wedding party fell into the Indus River in Pakistan's northeastern Gilgit-Baltistan region.

Lax safety measures

Naik Alam, a senior police official from the area, said the driver appeared to have been speeding when he lost control at a curve .

The groom's family had travelled from Punjab, more than 500 kilometres (300 miles) away, for the wedding and were returning home when the accident happened.

Road accidents with high fatalities are common in Pakistan, where safety measures are lax, driver training is poor, and transport infrastructure is often decrepit.

In Balochistan in August, 12 men died when their bus crashed into a ravine on the Makran Coastal Highway.

In another accident that month, 24 people on board a bus were killed when it plunged into a ravine near the town of Azad Pattan on the border between Punjab province and Pakistan-administered Kashmir.