Staff from 16 public transport companies in Portugal walked out today in protest at the government's moves to cut a public deficit, bringing traffic across Portugal's biggest cities to a standstill.

Urban bus companies' employees went on strike Tuesday, joining staff of the Portuguese rail company who had begun a three-day walk out on Monday in opposition to the Socialist government's plans to freeze civil servants' pay.

In Lisbon, even river transport was cut off at at rush hour, adding further strain on the roads as commuters turned to their cars to get to work, local media reported.

The northern Portuguese cities of Porto and Braga were also hit by the strike, although Porto's metro service, like Lisbon's, did not joined in the strike.

Portugal's government has imposed a four-year freeze on civil servants' pay in a bid to cut the country's public deficit from 8.3 percent of gross domestic product (GDP) in 2010 to 2.8 percent in 2013.

It is also planning to privatise several state-owned companies, thereby adding 6.0 billion euros (8.0 billion dollars) to its revenues, including 1.2 billion this year.

The government has projected that public debt would reach 142 billion euros, or 86 percent of GDP this year.

Portugal's debt has sparked fears that it could soon face the same problems as heavily-indebted Greece, which is now desperately trying to secure IMF and eurozone loans to avert default.

The Lisbon stock exchange fell by more than three percent while the interest rate demanded by investors to hold Portuguese 10-year debt jumped above five percent on Monday, making it more expensive for the government to raise funds.