A group of about 150 trade union protesters blocked entrances to the Athens stock exchange building on Tuesday but bourse officials said they expected trade to go ahead normally.

There is a back-up capacity, an alternative mechanism that enables electronic trading to go ahead normally, Athens stock exchange Vice-Chairman Socrates Lazaridis told Reuters.

Already 101 terminals have logged on to the trading system, he said. The exchange operates through remote electronic trading and does not have a physical trading floor, although some staff need to report to work to keep systems running, officials said.

Trading is due to start at 0830 GMT.

The protests was being conducted by Greek communist workers' group PAME.

Greece has seen a string of one-day strikes in the last few months to protest against austerity measures as the government struggles to cut a huge budget deficit; major public and private sector unions plan a one-day strike this Wednesday.

However, public opinion polls show the government has considerable support; a poll by Marc for Sunday's Ethnos newspaper showed 57.6 percent considered belt-tightening steps went in the right direction, while 75.8 percent thought there should be no strike action until the debt crisis had passed.

(Reporting by George Georgiopoulos; Editing by Susan Fenton and Andrew Torchia)