The 7.2 magnitude quake on Saturday destroyed thousands of homes and buildings in a Caribbean nation which is still clawing its way back from another major tremor 11 years ago and is reeling from the assassination of its president last month.

Southwestern Haiti bore the brunt of the blow, especially in the region in and around the town of Les Cayes. Haiti's Civil Protection Agency said the toll from the disaster had climbed from 724 to 1297 and the hospitals that were still functioning were struggling to cope with some 5700 injured people registered so far.

The challenge facing Haiti has been exacerbated by the coronavirus pandemic, a severe economic downturn aggravated by fierce gang violence, and a political crisis that has engulfed the troubled nation after the assassination of President Jovenel Moise on July 7.

Churches, hotels, hospitals and schools were badly damaged or destroyed, while the walls of a prison were rent open by the violent shudders that convulsed Haiti.

In Les Cayes, a seafront town of about 90,000 people, rescuers in red hard hats and blue overalls pulled bodies from the tangled wreckage of one building, as a yellow mechanical excavator nearby helped to shift the rubble.

"We must work together to provide rapid and effective responses to this extremely serious situation," said Haiti's Prime Minister Ariel Henry, who had flown to Les Cayes.

Nearby countries, including the Dominican Republic and Mexico, rushed to send desperately needed food and medicines by air and across Haiti's land border.

The United States has dispatched vital supplies and deployed a 65-person search-and-rescue team with specialised equipment.

From the Vatican, Pope Francis urged the international community to show support swiftly.

Haiti's government appealed to aid organisations against setting up makeshift camps and urged them to work through the planning ministry, an apparent attempt to avoid the mistakes made following the devastating 2010 earthquake that killed tens of thousands of people.

The rescue and aid efforts will be complicated by Tropical Storm Grace, which is expected to lash Haiti with heavy rainfall on Monday.

Access to the worst-hit areas was complicated by a deterioration in law and order that has left key access roads in parts of Haiti in the hands of gangs.

Following Moise's assassination, which authorities have alleged was carried out by a group of largely Colombian mercenaries and Haitian accomplices, Prime Minister Henry said officials would aim to hold elections for a new president as soon as possible.

However, reports this week suggested the vote initially earmarked for September would not take place until November. The chaos unleashed by Saturday's disaster is likely to make the task of holding prompt elections harder still.

Australian Associated Press