Striking Greek subway workers have trickled back to work after the government threatened them with arrest, ending a nine-day walkout that paralysed public transport in Athens.

Traffic slowly resumed on Athens' subway lines on Friday afternoon after workers protesting wage cuts were served orders to return to work or face jail, the first time the government has invoked such legislation since it took power in June.

The showdown had turned into the latest test for Greece's fragile three-party ruling coalition as it faces down unions to try to implement austerity measures demanded by foreign lenders as the price for bailout funds.

"The workers who were handed the notice didn't have a choice. We are exploring legal options," said Manthos Tsakos, general secretary of the main subway workers' union.

Earlier in the day, some 300 riot police stormed a train depot to break up the sit-in and briefly detained at least 10 workers.

The radical leftist opposition Syriza party, which is leading in some opinion polls, said the police intervention was a "barbaric" attack on workers' rights.

Eager to show lenders and Greeks that it is determined to implement promised reforms, Prime Minister Antonis Samaras has taken a hard line on the strikers despite facing criticism from one of his own coalition partners.

"When labour action is judged illegal and abusive, the law has to be implemented," government spokesman Simos
Kedikoglou told state television.

"Everyone has made sacrifices and no one can ask to be made an exception."

Gridlock and exasperation

Other transport unions held strikes in solidarity with subway workers on Friday, leaving Athens without bus, tram, trolleybus or rail services, and causing gridlock across the city.

Traffic ground to a halt in the capital, fuelling public anger against the strike which affected more than a million commuters in a city of 5 million people.

But commuters, worn down by years of frequent strikes and exasperated by the long wait for a taxi to work, said the strike only made life more difficult for them. 

"This week has been hell. How can they [train workers] expect people to be on their side when they do this to us? It's very difficult to have any sympathy for them," said 50-year-old Dionisis Kefalas.

Subway employees oppose being included in a unified wage scheme for public sector workers drawn up under an austerity programme that would slash their salaries.

Under the emergency law invoked, which is meant to be used in times of war, natural disaster or risks to public health, workers can be arrested and jailed for up to five years.