The vehicle, with nearly 48 passengers on board, was traveling from Quetta to Karachi.
Fresh fighting comes less than a week after cross-border shelling and gunfire killed eight Pakistani civilians and one Afghan soldier near the same Chaman-Spin Boldak crossing.
The attack comes a week after Tehrik-i-Taliban Pakistan ended a ceasefire with the government this week.
The border crossing was reopened after dialogue between Pakistani government and Afghan Taliban officials, says the deputy commissioner of Pakistan’s town of Chaman, which borders Afghanistan’s Spin Boldak district.
The crash took place in the district of Hernai, about 150 kilometres (90 miles) north of Quetta, the capital of Balochistan province.
Floodwaters are receding and the Indus River, which had swelled until earlier this month, is now rushing at "normal" levels towards the Arabian Sea, officials in the worst-hit southern province say.
Toll rises with 57 more deaths, 25 among them children, and officials say floods inundating a third of the South Asian country were preceded by four heatwaves and multiple raging forest fires provoked by climate crisis.
More than two million acres of agricultural land have been flooded and government is close to a deal to import vegetables and other edible goods from Iran and Afghanistan, officials say.
The consignments sent by the Turkish government, as part of a commitment by President Recep Tayyip Erdogan, include tents, medicines, food items and other essentials.
Scores of people were killed and dozens went missing in the past 24 hours as monsoon downpours and roaring floodwaters continued to pound the country.
Pakistan's government has set up aid and relief camps in regions hit by 133 percent more rain than the average for the past 30 years.
Baloch insurgents say they shot down the "low flying helicopter" with an anti-aircraft weapon, however, a senior military official dismissed the insurgents' claim as propaganda and fake news.
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