The U.S. and other governments urged visitors to exercise caution as Greek riots are giving violent demonstrations in capital Athens, Thessaloniki and in other cities and islands.

According to reports, Riots have raged in at least 10 cities and the cost of damage to shops and businesses in Athens alone is estimated at about 200 million euros ($259 million).

Moreover, a strike by Greece’s two largest labor unions closed Athens International Airport and also disrupted public transport and other services.

Thousands marched on parliament on Wednesday in a union rally at economic and social policy, which quickly turned violent. Police fired teargas and protesters responded with stones, bottles and sticks.

The strike had been planned before five days of riots sparked by the shooting of a 15 year old teenager by police. Greece was already in turmoil before the strike with four days of widespread rioting. Massive damage caused by the rioting kept many stores closed on Wednesday.

Prime Minister Costas Karamanlis announced financial support for businesses damaged in five days of rioting. He also pledged to safeguard people from violence, but did not say how.

Opposition leaders have blasted the government amid the unrest, prompting Karamanlis to call for national unity in the face of existing widespread anger over the economy, jobs, and allegations of government corruption.

The leader of the left-wing opposition party SYRIZA has called for protesters to topple the government, but Karamanlis ruled out early elections.

The unrest is the worst in Greece since the aftermath of military rule in 1974.