An American nurse and her child kidnapped in Haiti have been freed after nearly two weeks in captivity, her employer has said.

"It is with a heart of gratitude and immense joy that we at El Roi Haiti confirm the safe release of our staff member and friend, Alix Dorsainvil and her child who were held hostage in Port au Prince, Haiti," the aid group said in a statement on Wednesday.

"We are so thankful for everyone who joined us in prayer and supported us during this crisis."

Dorsainvil and her child were kidnapped near Haiti's capital Port-au-Prince on July 27, just days after the US government ordered its nonessential personnel out of the impoverished Caribbean country due to spiraling insecurity.

She is the wife of the group's director, who is Haitian, and the mother and child were taken from the El Roi campus "while serving in our community ministry," the group said when it first announced her abduction.

It described her at the time as a "deeply compassionate and loving person who considers Haiti her home and the Haitian people her friends and family."

The group did not provide details on the release or who was involved in securing the freedom of Dorsainvil and her child, and urged people not to try to contact the family.

"We will continue to release information as appropriate on our website," El Roi said.

The kidnapping came after the US State Department issued an updated travel advisory saying Americans in Haiti should depart "as soon as possible ... in light of the current security situation and infrastructure challenges."

Gangs control most of the capital and terrorize the population with kidnappings, rape and murder.