Trucks filled with riot police rolled behind the demonstrators as they jogged to the palace from a gathering place several miles (kilometers) away and chanted insults at Preval and his wife.
There was an anti-Preval demonstration last week in the coastal town of Jacmel, and many people have criticized the president's low profile in the chaos that followed the earthquake, but this was the strongest showing of opposition to the Haitian leader since the catastrophe. Protesters accused him of using the destruction as a pretext to stay in office beyond his term.
"He is profiting from this disaster in order to stay in power," said Herve Santilus, 39, a sociologist who was laid off a few weeks after the magnitude-7 quake struck and has not been able to find work since.
Some protesters wrapped the Haitian flag around themselves and carried water to sustain themselves through what was expected to be a daylong protest.
Police shot into the air as people in the crowd threw rocks. Other shots also were fired, but it was not clear by whom. There were no apparent injuries.
"Preval has used the drama that our county went through and turned it into an opportunity for himself," said Claudy Louis, 29, a schoolteacher. "Instead of looking out for the people, he quickly hatched a plan to benefit the small group of people around him, the bourgeoisie."
Small bands of protesters gathered in other cities including Petionville, where about a dozen young men played drums and blew horns to get attention.
A couple hundred government workers clutching pick axes and shovels also gathered nearby at the Champ de Mars national mall to demand that the U.S. Agency for International Development pay them money they said they were owed for clearing earthquake rubble.
An estimated 230,000 people died in the 40-second quake.
Discontent over government policy and the squalor at makeshift camps has increased recently.
Preval announced last week he would stay in office up to three months past the end of his term, on Feb. 7, 2011, if the presidential election is delayed. Officials are struggling to hold the election as scheduled this fall. The quake destroyed the election agency's headquarters and records and killed or displaced about 1.6 million voters.
"I want to establish stability in this country," Preval said.
Parliament approved the measure late last week, though opposition lawmakers called it unconstitutional and compared Preval to brutal dictators of Haiti's past.
Opposition leaders also are livid about an 18-month emergency period approved by Parliament, during which $9.9 billion in foreign reconstruction money will be directed by a commission headed by former U.S. President Bill Clinton and Prime Minister Jean-Max Bellerive.