Medan – Five people were seriously injured on Thursday in a clash between riot police and workers demanding a pay rise near the Indonesian city of Medan, witnesses and hospital sources said.

Police fired blanks at around 100 workers striking near a steel factory just outside the city on Sumatra island. Dozens of police were assisted by around 300 youths carrying knives and spears. The clash followed a series of protests near the factory of steel firm PT Gunung Dahapi.

"Suddenly the youths and the security forces attacked us," said one worker. Hospital sources said one of the five injured was in critical condition.

Worker protests have become common around Medan, an industrial city 1,425 km northwest of Jakarta, as Indonesia endures its worst economic crisis in three decades. Several have turned violent.