PORT-AU-PRINCE - Haiti's president said on Wednesday he feared thousands had died in a major earthquake that wrecked the presidential palace, schools, hospitals and hillside shanties, leaving the Caribbean nation appealing for international help.

A five-story U.N. headquarters building was also brought down by Tuesday's 7.0 magnitude quake, the most powerful to hit Haiti in more than 200 years according to the U.S. Geological Survey.

President Rene Preval called the damage unimaginable and told The Miami Herald he believed thousands were dead. He described stepping over dead bodies and hearing the cries of those trapped inside the collapsed Parliament, where the senate president was among those pinned under the wreckage.

There are a lot of schools that have a lot of dead people in them, he told the Herald. All of the hospitals are packed with people. It is a catastrophe.

Scenes of chaos gripped the streets of the capital, Port-au-Prince, with people sobbing and wandering dazed amid the rubble of the impoverished city.

The presidential palace lay in ruins, its domes fallen on top of flattened walls. Preval and his wife were not inside when the quake hit.

The quake's epicenter was only 10 miles (16 km) from Port-au-Prince. About 4 million people live in the city and surrounding area. Many people slept outside on the ground, away from weakened walls, as aftershocks as powerful as 5.9 rattled the city throughout the night and into Wednesday.

Reports on casualties and damage were slow to emerge due to communication outages.

Many were feared dead when the U.N. building collapsed.
U.N. Secretary-General Ban Ki-moon said the missing included the chief of the U.N. mission in Haiti, Hedi Annabi, but he could not confirm reports Annabi had died. He said 100 to 150 people were in the building when the quake struck.

(Additional reporting by Sophie Hardach, Raymond Colitt, Alister Bull, David Morgan, Jane Sutton, Phil Barbara, Patrick Worsnip; Writing by Jane Sutton and Pascal Fletcher; Editing by David Storey)