Haitian President Michel Martelly has left office at the end of his term amid tension over how he is to be replaced.
No successor has yet been chosen as opposition supporters challenge a deal to select an interim leader.
The first day of carnival has been called off over the threat of more opposition protests.
Haiti, the poorest country in the Americas, is still struggling to recover from a huge earthquake in 2010.
The last-minute deal aims to prevent the country from plunging into an immediate power vacuum.
In a speech, Michel Martelly said his biggest regret was that January’s presidential election had been postponed.
It will now be held on April 24, with a new president due to be sworn in on May 14.
Under the latest agreement, parliament will elect an interim president and install a transitional government for a four-month term.
Michel Martelly is constitutionally barred from seeking re-election but has thrown his weight behind Jovenel Moise, a banana exporter who won the first round of the presidential election in November.
However, the result has been contested by the opposition challenger, Jude Celestin.
Jude Celestin accused the electoral authorities of favoring Jovenel Moise and threatened to pull out of the runoff vote.
PM Evans Paul – who is due to remain in his post until parliament agrees his replacement – has appealed for calm.
On February 5, protesters beat a man to death in the capital, Port-au-Prince, in a clash with ex-soldiers.