Protesters display placards as they prepare to march towards Manila's financial district, 12 Dec 2008

Thousands of people in the Philippines have demonstrated against a move to revise the constitution, which they say could extend the presidential term in office.

Left-wing lawmakers and religious groups joined opposition protesters in a march through central Manila Friday, with police on high alert.

Supporters of President Gloria Arroyo have held public hearings in congress on amending the constitution. The president's opponents said the amendments would enable her to stay in office beyond 2010, when her six-year term expires.

President Arroyo has survived several coup attempts and efforts to impeach her on charges of corruption.

In recent decades, massive street protests in the Philippines have led to the ousters of former presidents Ferdinand Marcos and Joseph Estrada.

Mr. Estrada has warned President Arroyo to distance herself from moves to change the constitution to prevent street protests from turning violent.

The Philippine constitution allows only one six-year presidential term. President Arroyo replaced Mr. Estrada after he was deposed in 2001. She was able to run in the 2004 presidential election because she had served no longer than four years as interim president.

Some information for this report was provided by AFP, AP and Reuters.