The massive tremor struck around five pm local time prompting a brief tsunami alert in neighbouring Caribbean islands.
Huge aftershocks added to the widespread panic.
With only a thousand hospital beds in the capital, international offers of aid have been rapidly pouring in.
The US Secretary of State, Hillary Clinton said: “the United States is offering our full assistance to Haiti and others in the region. We will be providing both civilian and military disaster relief and humanitarian assistance.”
As US rescue and recovery teams prepare to deploy other countries have also pledged food, shelter and medical relief.
Speaking in Caracas, Venezuela’s Foreign Minister, Nicolas Maduro said the his government planned to send a military aircraft with drinking water and food along with a team of 50 rescue workers.
The World Bank says it also plans to send a team to help Haiti assess damage and plan a recovery from its strongest earthquake in 200 years.