ATHENS (AFP) - Thousands of demonstrators took to the streets in Greece on Thursday as workers staged a nationwide strike to protest against the government's dramatic shutdown of public broadcaster ERT.

The protesters gathered outside ERT's offices in Athens and Thessaloniki to call on Prime Minister Antonis Samaras to reverse his decision to pull the plug on the broadcaster as part of sweeping cost-cutting measures.

ERT employees, stunned by the sudden loss of their jobs, were defiantly transmitting rogue broadcasts on the Internet and the Communist party television channel.

The government responded with the threat of legal action.

"Any broadcasts carrying ERT's signal are unauthorised... and can be sanctioned under the law," the finance ministry said in an email to operators, released by Greek media.

The 24-hour strike called by the major trade unions to support ERT workers saw trains and buses grinding to a halt and and left hospitals operating on emergency footing.

Air traffic controllers held a two-hour work stoppage while broadcast journalists were on an indefinite strike over the government's shock move.

"This has to stop," said Olga Papaiossif, a 41-year-old pre-school teacher as she protested in Athens.

"They want to sell everything in Greece, the TV, the water, everything. And in the rest of Europe too," she said.

Greek media on Thursday raised the prospect of early elections, warning that Prime Minister Samaras could have pushed his coalition allies too far this time.

The socialist and moderate leftist supporting his government are already facing internal pressure over the unpopular austerity measures Greece has been applying for a fourth year.

As if on cue, the state data agency on Thursday said the jobless rate had climbed to 27.4 per cent in the first three months of the year, from 26 per cent a year earlier.

"A solution in one week or elections," said liberal Kathimerini daily while centre-left Ta Nea spoke of "dangerous acrobatics."

"In case of a deadlock, the scenario of early elections becomes especially strong," Kathimerini said.

Samaras seemed to take a step back late on Wednesday after his coalition partners blasted the closure of ERT as "unacceptable".

A government source said the prime minister would call a meeting with his partners to confer on the issue.

Samaras had earlier defended the closure, saying: "We are eliminating a hotbed of opacity and waste."

The broadcaster's television and radio stations were abruptly pulled off air late Tuesday and its nearly 2,700 staff suspended.

The administration quickly presented legislation creating a new broadcaster called New Hellenic Radio, Internet and Television (NERIT) to replace the 60-year-old ERT.

The broadcaster will reopen with around half its current number of employees, officials said.

"You can't fix a car while it is running, you have to take it off the road," said government spokesman Simos Kedikoglou, promising a "restart" during the summer.