Haiti is under a state of seige with its borders and main airport closed.
The announcement came hours after President Jovenel Moïse was assassinated by unknown gunmen at his private residence in Pelerin, a wealthy suburb of the capital, Port-au-Prince.
Prime Minister Claude Joseph says he is now in charge of the country and has imposed martial law.
"I have just chaired an extraordinary council of ministers meeting and we have decided to declare a state of siege throughout the country." PM Claude Joseph said.
The announcement brings into fore the question of the prime minister's legitimacy. Moïse had been due to install Ariel Henry as prime minister on Wednesday after dismissing Claude Joseph. But it was Joseph who instead announced Moïse’s killing.
Analysts say that the interim president should be the chief justice according to the Haitian constitution. But the chief justice died of Covid in June. The political situation spells much of uncertainty.
Meanwhile, reactions to the development have continued to pour in. United Nations Security Council president, Nicolas de Riviere, said the council was deeply shocked by the assassination and will meet privately on Thursday morning.
While U.S. President Joe Biden condemned the attack and in a statement issued by the White House expressed condolences.
"We need a lot more information but it's very worrisome about the state of Haiti." Biden also said to a reporter.
Moïse’s wife, Martine the first lady, was injured in the attack and taken to a hospital for treatment. Her husband was elected in late 2016 and has been ruling by decree for more than a year.
The killing comes as an explosive climax to a period of political instability and division, and a rise in gang violence across the Caribbean country of 11 million inhabitants.