Traffic clogged roads out of the Thai capital Friday as tens of thousands of people fled ahead of a high tide expected to worsen floods that have inundated factories and prompted foreign governments to warn their citizens to stay away.

The main concern is that Bangkok’s Chao Phraya River will burst its banks over the weekend during the unusually high tide that begins Friday. Buildings across Bangkok have been sand-bagged for protection, and some vulnerable streets were nearly deserted.

Thailand’s worst flooding in half a century, caused in part by unusually heavy monsoon rain, has killed 377 people since mid-July and disrupted the lives of nearly 2.2 million, until now mostly in the north and central provinces.

Television footage showed cars and trucks bumper-to-bumper leaving the city and the main airport’s departure lounges packed, but the traffic department said it could not put an exact figure on the size of the Bangkok exodus because much of its monitoring equipment was under water.