At the time, the onset of industrialisation had sparked rapid development. Workers were forced to work long hours - 12 to 14 hours a day - with little pay and no benefits.

The Knights of Labour quickly garnered support from workers and other industries also set up unions.

On September 5, 1882, the Knights of Labour organised a parade in New York City.

Another parade was held in 1884 and the Knights passed a resolution to make these parades an annual event. In the same year, the first Monday in September was designated as a 'workingmen's holiday'.

But the improvement of labour rights fell short of the workers' expectations. On May 1, 1886, the American Labour Federation declared a national strike to demand an eight-hour workday. Hundreds of thousands of labourers took part. Over the next few days, an increasing number of people joined the strike, ending in a mass rally in Chicago's Haymarket Square on May 4.

Towards the end of the rally, someone threw a bomb into the crowd, killing a police officer and injuring others. The police, in turn, opened fire, killing several demonstrators and injuring hundreds of others. Several labour leaders were brought to trial and imprisoned or hanged despite a lack of evidence.

To commemorate the riots, May 1 - the day of the original demonstrations - was set aside as a recognition of worker solidarity in many countries which face labour problems. Most countries, including Hong Kong and the mainland, celebrate Labour Day on May 1, but in the US and Canada Labour Day falls on the first Monday of September.

A survey conducted by Hong Kong Institute of Human Resource Management last year revealed that the local workers worked on average between 53 to 57 hours per week, including overtime.