A 24-hour strike in Portugal against proposed austerity measures has grounded flights and halted public transport. Hundreds of thousands of workers took part in the action, including air traffic controllers, metro workers, teachers and hospital staff.

A march in the capital, Lisbon, attracted thousands of protesters.

Parliament will vote next week on a deficit reduction plan being imposed as a result of an international bailout.

Portugal is getting 78bn euros (£67bn; $104bn) in emergency funds from the EU and the International Monetary Fund (IMF)

In a separate development on Thursday, the credit ratings agency Fitch downgraded Portugal's debt to junk status, blaming Lisbon's "large fiscal imbalances" as well as the "adverse macroeconomic outlook".

The strike, supported by Portugal's two main labour unions, was thought to be among the biggest in Portugal's history, where mass industrial action is rare.

"There is a strong sentiment of outrage," said Manuel Carvalho da Silva, Secretary General of the CGTP union, who described the general strike as a "red card" for the government.

Hospitals provided only emergency care, many schools were closed and public transport was severely disrupted. The Lisbon metro was shut. Rubbish collections and postal deliveries were also hit.

Airlines were particularly badly affected and the airports at Lisbon, Faro and Porto were largely deserted.

The strike passed off peacefully on the whole, although three tax offices were attacked.

Joao Proenca, leader of the country's second main union, UGT, said he hoped the government would pay attention to the effects of the strike.

But Parliamentary Affairs Minister Miguel Relvas insisted that the country had no other choice but to adopt austerity measures.

"We have a current situation in Portugal that requires us to ask for external help and we can only recover from this situation by being rigorous and demanding," he told reporters.

The government proposes spending cuts across a broad range of public services, including health care and the armed forces, as well as tax hikes.

Also planned is the elimination of Christmas and holiday bonuses, equal to about a month's pay for most public sector workers, and allowing private firms to extend the work day by 30 minutes without overtime pay.

With the unemployment rate higher than 12% and the economy forecast to contract next year, Prime Minister Pedro Passos Coelho, whose conservative government came to power in June, has said he has to cut public spending.

His governing coalition has a majority in parliament so the final vote next week on the 2012 budget is expected to pass.

Portugal was the third EU country after Greece and the Irish Republic to receive a bailout. Further instalments of the emergency loans could be withheld if it does not meet targets for deficit reduction.

This is only the third general strike since Portugal became a democracy in the 1970s.

The right-of-centre government's budget for 2012, currently going through parliament, includes the suspension of holiday and Christmas bonuses for most public sector workers and many pensioners.

Hot spots included transport, hospitals, schools and rubbish collection - where unions claim a total stoppage in many places.

TAP Air Portugal have cancelled 121 services - although half a dozen flights were still operating between Portugal's far-flung islands. Hundreds of other flights have been grounded, but air traffic controllers are assuring overflights.

In general, the action has been peaceful. But there have been clashes over the definition of minimum services that unions are obliged to guarantee in key sectors.

In Oeiras, near Lisbon, police waded into picket lines to allow three rubbish trucks to leave a depot. Strike supporters are also reported to have attempted to block a railway line out of the capital.

Petrol bombs have apparently been thrown into the windows of two tax offices in the Greater Lisbon area, and a tin of paint thrown into another. The offices were closed and no-one was hurt.

Most private companies are not directly affected, but workers at a few large, unionised exporters are downing tools.