Haiti's security forces were locked in a fierce gun battle on Wednesday with assailants who assassinated President Jovenel Moise at his home overnight, plunging the already impoverished, violence-wracked nation deeper into chaos.

The police had killed four of the "mercenaries" and captured two more, Police General Director Leon Charles said in televised comments late on Wednesday, adding that security forces would not rest until they had all been dealt with.

The government declared a two-week state of emergency to help it hunt down the assassins.