An armed criminal group in Haiti has kidnapped a group of US missionaries and children, according to media reports.

AFP news agency said an alert had been sent out by US non-profit Christian Aid Ministries to its supporters asking for prayer. 

The kidnapping occurred in the Ganthier area near the capital of Port-au-Prince on Saturday morning as the group returned from building an orphanage.

The area has been a hotspot for kidnappings for ransom by criminal gangs, with victims including a priest and nun earlier this year. 

The missionaries are reported to have been ordered off a bus and seized while en route to the capital's Toussaint Louverture airport, where they were to catch a flight home to the US.

The Washington Post reports that one member of the group sent a desperate plea for prayer via WhatsApp while the kidnapping was underway. 

"Please pray for us!! We are being held hostage, they kidnapped our driver. Pray pray pray. We don't know where they are taking us," they said. 

Haiti has been in the grip of a power struggle since the killing of President Jovenel Moïse in July. The last few months have seen a deterioration in the security situation, with the challenges only compounded by a 7.2-magnitude earthquake in August that killed over 2,200 people. 

Commenting on the reports of the kidnapping, a spokesperson for the Department of State told the Guardian: "The welfare and safety of US citizens abroad is one of the highest priorities of the Department of State."