Lebanese MPs have failed to convene to elect a new president as the term of the incumbent, Emile Lahoud, expires.
Members of the Western-backed majority had hoped to hold a vote, but the pro-Syrian opposition did not allow the session to achieve the quorum needed.
The crisis has raised fears of civil strife, including the possibility of rival administrations, as happened during the 15-year civil war.
Parliamentary speaker Nabih Berri said the vote would be held on 30 November.
Repeated attempts to elect a new president over the past two months have been scuppered by rivalry between the factions.
The term of Mr Lahoud, a pro-Syrian, ends at midnight on Friday.
Members of the ruling majority urged Mr Lahoud to leave the presidential palace tonight when his term formally expires.
"If he chooses to stay... it will be a crime against the constitution which is sanctioned by law," deputy speaker of parliament, Farid Makari, said, reading a statement from the ruling majority.
The tension was palpable on the streets as the crisis over electing the president came to a head, with the army deployed in force and schools closed, BBC Beirut correspondent Kim Ghattas says.
Check points have also been set up and the ministry of interior has suspended all firearm permits until further notice.
The election of a president requires a two-thirds majority, which means that the pro-Western ruling bloc - with its slim majority - could not force its preferred candidate through parliament.
Vote scheduled 1300 (1100 GMT) Friday but not held. Speaker sets vote for 30 November
President Emile Lahoud's term expires 2400 Friday
If the presidency become vacant, constitution says presidential powers passed to PM Fouad Siniora
But pro-Syrian President Lahoud wants to appoint army chief as president
According to Article 62 of the Lebanese constitution, if the presidency becomes vacant, presidential powers are automatically transferred to the anti-Syrian government of Prime Minister Fouad Siniora.
However, President Lahoud has vowed not to hand over power to Mr Siniora, and said he would name army chief General Michel Suleiman as his provisional successor instead.
The political deadlock has already led to the vote being postponed four times since 25 September.
The issue has also turned into a regional and international affair.
The US, Russia, Syria and Iran are all intensely involved and there has been a lot of diplomatic shuttling between Damascus, Moscow, Tehran and Paris ahead of the end of Mr Lahoud's term.