Land and sea border checks between them and the other Schengen countries are now abolished, while air borders are set to follow on 30 March 2008.

Practically it means that as of today, "people can travel hassle-free between 24 countries of the Schengen area without internal land and sea border controls- from Portugal to Poland and from Greece to Finland", EU justice commissioner Franco Frattini said in a statement.

"An area of 24 countries without internal borders is a unique and historical achievement. I feel very proud and privileged to have been involved in making it happen", he added.

Meanwhile, celebrations were held and are to be held throughout Friday on several border points to mark the occasion.

However, some were more enthusiastic than others. While Slovaks were celebrating until late in the night on Friday at the country's border with ‘old' member state Austria, no celebrations could be noted on the Austrian side.

A recent poll carried out in Austria showed 75% of its citizens opposed the lifting of barriers, according to the BBC.

Fears of crime wave

While many EU citizens are looking forward to the free movement regime, others have expressed fears that it will lead to an increase of crime and illegal immigration.

Politicians dismissed the fears, however.

Schengen "is not about criminality, it is not about insecurity or fear. It is a bigger zone of peace, security and stability", Austrian chancellor Alfred Gusenbauer said in Slovakia on Thursday (20 December).

"It's an historic occasion following the destruction by the first and second world wars and the division of our continent by the Iron Curtain (…) Free borders in a free Europe: who would have dared to even dream of that in 1985", Mr Gusenbauer added.

European Commission president Jose Manuel Barroso said: "Together we have overcome border controls as man-made obstacles to peace, freedom and unity in Europe".

And what about EU neighbours?

While the enlargement of the Schengen area means that some 400 million EU citizens will now be able to travel more easily within it, it also constitutes a new burden for some EU neighbours.

The short stay Schengen visa currently costs €60 for third country nationals and is a significant increase for some non-EU citizens.

Until now, Belarussians have paid €5 for a trip to neighbouring Lithuania.

Other EU neighbours - the Ukraine, Moldova, Bosnia-Herzegovina, Serbia, Montenegro, the Former Yugoslav Republic of Macedonia and Albania – have concluded visa facilitation agreements with the EU, which are expected to enter into force on 1 January 2008.

Russian citizens are also covered by such a deal, which entered into force in June this year.

Under the visa facilitation agreements, citizens of these countries can obtain a Schengen visa for €35, while certain categories of citizens are exempted from the fee.

The Schengen area was established in 1985 and named after the small Luxembourg village where it was signed by Germany, the Benelux countries and France.

The nine new countries joined the 15 others already in Schengen - thirteen EU states excluding the UK and Ireland which preferred to stay out, but including Norway and Iceland.

Non-EU member Switzerland is also to become a member of the Schengen area next year, while three EU states – Cyprus, Bulgaria and Romania have still to meet the necessary requirements.

It is not yet known when they will join the EU's borderless zone, but Cyprus is expected to do so around 2009, while Bulgaria and Romania are hoping to follow suit by 2011.