Police said the minivan driver lost control and ploughed through a central reservation into oncoming traffic in the eastern province of Chonburi. Both vehicles burst into flames.
One dead, 10 injured in road accident
"Twenty-five people were killed in the road accident," Police Lieutenant Colonel Wiroj Jamjamras at Ban Bueng provincial police station told AFP, adding two toddlers were among the dead.
"The victims were killed by fire or the impact," he added.
Wiroj said 15 people were inside the minivan while 12 passengers were packed into the pickup truck.
Two were injured but are expected to survive, he added.
Footage broadcast on Channel 3 showed firefighters tackling the burning, twisted wreckage of the two vehicles.
Despite relatively good infrastructure, Thailand has the world's second most dangerous roads in terms of per capita deaths, according to data collected by the World Health Organization in a 2015 report.
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Fatalities tend to rise in the New Year week and during Songkran, a religious festival in April, when millions of low-paid workers return to the countryside from their city jobs to see family.
Both weeks are dubbed the "Seven Deadly Days" in Thai media, with the government keeping a daily death tally during those two periods to try to encourage better road safety.
As of Sunday -- the fourth day of the country's New Year holiday week -- 280 people had died on Thailand's roads, a 10 percent increase on last year.
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Some 43 percent of the recorded smashes involved drink-driving and 82 percent involved motorbikes.
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