Six migrant workers from Burma were killed when a double-decker bus they were travelling in crashed into a ditch in Thailand, the second fatal accident in as many weeks involving migrants.

Up to 3 million people from poorer neighbour Burma work in Thailand, many in menial jobs, with their remittances home contributing 5 percent of gross domestic product, the World Bank estimates.

Some rights groups say the migrant workers face harsh working conditions, and Thailand tightened rules for work permits last year.

The bus was travelling late on Monday from the border town of Mae Sot to the province of Chachoengsao, a farming hub near Bangkok, the capital.

“Six people died and 30 were injured,” national police spokesman Kissana Phatanacharoen told Reuters, adding that the driver, who told police the brakes were not working, had been charged with causing death by reckless driving.

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Last month, a fire on board a bus in western Thailand killed 20 migrant workers.

The accidents come amid preparations for the Songkran festival that ushers in the traditional Thai New Year.

The festival, which can be a raucous affair, brings a spurt in the number of road deaths from careless driving, including drunk driving, which successive governments have targeted with vigorous road safety campaigns.

Thailand’s roads rank as the world’s deadliest after Libya’s, the World Health Organization says in its most recent study.