Greek police on Friday detained three people who had been sought since Wednesday as key suspects in the shooting of dozens migrant fieldworkers in western Greece during a dispute over back pay, local media reported.

The police launched a manhunt for the three, including a 27-year-old supervisor who allegedly fired at a group of some 200 protesting workers with a shotgun on Wednesday, after a 28 Bangladeshi strawberries pickers were injured in the shoot-out.

The same person has a record of abusing workers and is awaiting trial for dragging a migrant along his car in the same area a year ago, according to police and judicial authorities.

The unprecedented shooting has been strongly denounced as racist and inhumane by Greece's government, political parties and the public.

On a visit to the city on Friday Public Order Minister Nikos Dendias reiterated pledges for "swift and exemplary" punishment of the people responsible, stressing that the victims treated in hospital and eye witnesses should not fear deportation.

Several of the some 5,000 migrant workers in the area do not have residence permits and are working without insurance for lower salaries compared to Greeks in difficult conditions for years without protesting for fear of deportation, labor unions and human rights groups claimed.

The Greek government promised a thorough investigation into working conditions at the region, as well as into any cases of racist attacks against the workers.

Racist attacks are on the rise in recent years across Greece, as a small percentage of recession-hit Greeks embrace the xenophobic rhetoric of ultra-right groups, political analysts noted.

The far-right Golden Dawn party which entered the parliament for first time during last year's general elections also condemned the shooting incident, while calling for the replacement of all foreign workers by Greeks and the immediate deportation of all illegal immigrants.