Central Chile has been rocked by three strong aftershocks, spreading panick among residents, already traumatised by last Saturday's devastating earthquake. The aftershocks leveled more buildings in the area.

A first magnitude 6.2 aftershock jolted people in and around the city of Concepción awake at 6:20 am local time. It came six days after an earthquake registering 8.8 on the Richter scale. Over 800 people were killed in the tsunami waves which followed. Some two million people were left homeless.

This morning' s tremor was followed by a 6.8-magnitude tremor, the most powerful of more than 200 to rattle Chile since Saturday. The third tremor registered 6.6 on the Richter scale.

The latest tremors have caused buildings already damaged by the disaster to collapse, although there are no reports more casualties.

United Nations Secretary General Ban Ki-moon was due to begin a two-day visit to assess the damage and relief needs in the quake zone.

He also planned to meet outgoing President Michelle Bachelet, who has called for a period of national mourning. Discrepancies have emerged over the death toll, which some claim could be lower than official figures.