Twenty-one people were injured when a bus carrying 63 high school pupils and four teachers crashed on the Ioannina-Rio road near the town of Amphilochia in western Greece yesterday afternoon. Two of the children and one teacher were the only ones to sustain serious injuries but were not in danger, according to initial reports. The group was returning to the northern Greek town of Kozani from a three-day excursion to Patras. The driver told police he lost control of the bus after one of the tyres burst. The bus went off the road, hitting a pole and a tree. Last April 13 in the Vale of Tempe on the highway linking Athens and Thessaloniki 21 teenagers were killed when a truck collided with a bus filled with high school students on their way home from a field trip. Their annual memorial service was held yesterday.