Police spokesman Marek Kapusta said today that the driver probably fell asleep behind the wheel, causing the bus to cross into the opposite lane before landing in a ditch and hitting a tree near the village of Gorzno-Kolonia, about 75 kilometres southeast of Warsaw.
Kapusta said the passengers were probably all Ukrainian.
He said that three people were instantly killed and another two died in a hospital, while 25 other people, including 2 children, remain hospitalised.