Greek authorities have launched roundup operations of illegal immigrants in Athens, detaining some 700 persons, according to police figures on Friday, as special centres to house migrants to be deported are under construction.

The Greek government announced a few days ago a two-year plan to combat the chronic problem of illegal migration that adds burden to the debt-ridden country, with the creation of about 30 detention centres nationwide starting as soon as next week.

As preparation works in three such centres are under way, police started rounding up some of the 130,000 migrants who enter Greece illegally every year over the past two decades, mainly from Africa and Asia, according to official data.

Some 30 people detained during the roundup operations were also charged with sales of counterfeit products, burglaries, drug trading and prostitution.

The plan has caused reactions by part of Greek society. Critics raise concerns over the living conditions of the immigrants in the detention centres and whether the plan will resolve the issue.

Citizen's Protection Minister Michalis Chryssohoidis argues that without a plan to tackle the problem, Greece is threatened to be excluded from the European Schengen common travel zone.

European counterparts have criticized the country repeatedly of ineffective policies to counter the issue, as Greece has become a main transit point of illegal migrants to Europe in recent years.

According to estimates by Greek officials, approximately one million illegal immigrants live at the moment in Greece, a country of some 11 million inhabitants.

Local political analysts noted that the plan was launched ahead of the early general elections due late April or early May, under pressure by rightist groups.