Barnaby Phillips, Al Jazeera's correspondent in Athens, said a number of high profile injuries in the protests sparked "mayhem" in the capital.
"A prominent union leader was seen being punched in the face, apparently by another member of the crowd," Phillips said.
"And then a man called Manolis Glezos, very well-known in Greece, a sort of 'grand old man of the left', was seen being carried away injured, it's not sure how.
"Those high profile injuries seem to have inflamed the crowd and led to 45 minutes of mayhem in the city centre."
He added that consensus in Greece for the austerity measures apepared to be fraying, making a difficult situation for George Papandreou, the Greek prime minister.
Papandreou is currently embarking on a diplomatic quest for concrete support from European leaders to ease his country's debt crisis.
He has already ruffled Europe's feathers by warning that Greece could request financial help from the International Monetary Fund unless the EU details potential emergency support.
Jean-Claude Juncker, head of the group of eurozone finance ministers, said after meeting the Greek prime minister in Luxembourg on Friday that "we have to deal with the problem as a euro area".
He said it was acceptable for the IMF to offer technical assistance, but insisted that "as the chairman of the euro group I'd like to exclude any further involvement of the IMF".
Papandreou, who is due to meet Angela Merkel, the German chancellor, later on Friday, has said Greece needs "support" from Europe "so that we can borrow money under reasonable conditions".
Earlier, Rainer Bruederle, Germany's economy minister, said Berlin had no intention of offering Greece "one cent" in aid.
Friday's strike saw state schools closed, while hospitals functioned with emergency staff and all Athens public transport was idle.
George Papaconstantinou, the Greek finance minister, said the belt-tightening would work if unswervingly enforced.
"In emergencies, governments take emergency measures," he told politicians during an austerity law debate.
"Will we succeed? Yes, we will. Will we have to take further measures? No, provided we implement the programme we have submitted. And we will."