At least 50 people were killed when a gas tanker exploded in the Haitian city of Cap-Haitien yesterday morning, according to a local official, with overwhelmed local medics saying the toll was feared to rise.

"I saw on the scene between 50 and 54 people burned alive," Deputy Mayor Patrick Almonor said. "It is impossible to identify them."

Almonor also said "about 20" houses in the area were set ablaze by the explosion.

"We can't yet give details on the number of victims inside the houses," he said.

Nearby Justinien University Hospital was overwhelmed with patients as the injured were transported to the facility.

"We don't have the ability to treat the number of seriously burned people," a nurse told AFP.

"I'm afraid we won't be able to save them all," she said.

Haitian Prime Minister Ariel Henry said the explosion left "around 40 people" dead and dozens injured, as he decreed three days of national mourning.

Ariel said field hospitals would be rapidly deployed to help care for the blast victims.

According to Almonor, it appeared the truck driver lost control as it swerved to avoid a motorcycle taxi and the tanker flipped over.

Almonor said fuel spilled onto the road and pedestrians rushed to collect the tanker's gas, which is currently in short supply as Haiti grapples with a severe fuel shortage caused by the tightening grip of criminal gangs on the capital Port-au-Prince.