Police have clashed with thousands of protestors in the Hungarian capital Budapest.
Water cannon, rubber bullets and teargas have been used to disperse demonstrations across the city, with one group of about 1,000 protestors attempting to reach the parliament building.
It is understood at least 40 people have been injured, none seriously.
A number of foreign dignitaries are in Budapest to attend celebrations marking the 50th anniversary of the 1956 anti-Soviet uprising.
The anniversary has been marred by a month of protests following the admission by Socialist Prime Minister Ferenc Gyurcsany that he lied about the economy to win national elections in April.
The main right-wing opposition party, Fidesz, has boycotted all events involving the prime minister due to the recent scandal.
Hungarian leaders have been joined by 18 European presidents and two prime ministers, the king of Norway and NATO representatives in the celebrations, which started with the hoisting of the national flag.
President Mary McAleese was among those taking part.
The Hungarian uprising of 1956 was the first big challenge to Soviet rule in central Europe, and was one of the defining moments of the Cold War.
Soviet forces crushed the rebellion, which began on this day in 1956. Some 2,600 Hungarians died, more than 200 were executed for their role in the uprising and 200,000 fled the country.
The series of commemorative events is to culminate in a declaration read in parliament by Prime Minster Ferenc Gyurcsany.
Plaque unveiled in Co Clare
A special memorial plaque has been unveiled at a ceremony at the Knocklasheen Accommodation centre at Meelick in Co Clare to mark the 50th anniversary of the 1956 Hungarian uprising.
The plaque was unveiled by the Hungarian Ambassador to Ireland, Yanush Bolusha.
Up to 500 Hungarian refugees who arrived in Ireland were accommodated at the centre, which was a disused military camp at the time.
Some of the refugees returned to Hungary, many stayed and settled throughout Ireland. The centre currently hosts asylum seekers from Africa and Asia.
