The FBI will assist in the investigation and efforts to locate and free a group of US Christian missionaries who have been kidnapped and are being held by a criminal gang in Haiti, a US law enforcement official has said.

The Ohio-based Christian Aid Ministries organisation yesterday said a group of its missionaries had been kidnapped in Haiti. The group includes 16 Americans and one Canadian.

They were in Haiti to visit an orphanage when their bus was hijacked on Saturday outside the capital Port-au-Prince, according to accounts by other missionaries, amid a spike in kidnappings following the murder of President Jovenel Moise.

The incident is a further sign the Caribbean nation's gangs are growing increasingly brazen amid political and economic crises.

Specific details of the role the FBI will play in trying to free the missionaries were not immediately available. The FBI's national press office said in a statement it was referring questions on the kidnapping to the state department.

Representatives of key congressional committees overseeing foreign affairs and law enforcement said they had not been briefed on FBI involvement in efforts to locate and free the missionaries.

Meanwhile, a nationwide general strike emptied the streets of Port-au-Prince today, with organisers denouncing the rapidly disintegrating security situation highlighted by the kidnapping.

"It has been months since we appealed for help, and since we have had no security against kidnappings we have called for the population to suspend all activity," said the president of Haiti's Association of Owners and Drivers, Changeux Mehu.

"The bandits are going too far. They kidnap, they rape women, they do whatever they want. Enough."

Launched last week by business and professional groups in Port-au-Prince, the call for a strike took on additional resonance after the kidnapping.

"The kidnapping of the Americans shows that no one is safe in the country," Mr Mehu said. "We pay our taxes to the state.

"In return, what we ask is to have security, so that the country can function."

Armed gangs, which have controlled the poorer neighborhoods of Port-au-Prince for years, have tightened their grip on the city and the surrounding areas, where kidnappings have surged.

"Nature abhors a vacuum, so gangs take advantage of it to gain strength," said Gedeon Jean, director of the Center for Analysis and Research in Human Rights.

The United States in August issued a red alert on Haiti, urging Americans not to travel to the Caribbean nation because of rampant kidnapping, crime and civil unrest.

Additional reporting by AFP