The term of Lebanon's president has ended with no elected successor and a bitter dispute over who is in power.
Mr Lahoud left office refusing to recognise the PM's government
Before pro-Syrian President Emile Lahoud left the presidential palace at midnight (2200 GMT) he issued an order that the army should take over control.
But pro-Western PM Fouad Siniora rejected the move and says that under the constitution he and his cabinet are in temporary power.
The latest in a series of attempts to find a new president failed on Friday.
The president is elected by parliament, but a vote was scuppered after the pro-Syrian opposition did not allow the necessary quorum to be achieved. A new vote has been scheduled for 30 November.
Vote scheduled 1300 (1100 GMT) Friday but not held. Speaker sets vote for 30 November
President Emile Lahoud's term expires 0000 Saturday
If the presidency become vacant, constitution says presidential powers passed to PM Fouad Siniora
Mr Lahoud refused to recognise Mr Siniora's government and analysts say his security move was effectively a call for a state of emergency.
The US has urged all parties to remain calm and said that under the constitution the Lebanese cabinet should "temporarily assume executive powers and responsibilities until a new president is elected".
Shortly before midnight, Mr Lahoud, 71, walked out of the Baabda presidential palace as the national anthem played, ending nine years in office.
AFP news agency quoted him as telling reporters: "If they do not elect a new consensual president, with the required two-thirds majority, we have men who can stand up."
The BBC's Kim Ghattas in Beirut says that opponents of Mr Lahoud have been celebrating the departure of man they see as the last remnant of Syrian influence over the country.
She says the country appears to be in the ultimate political limbo, with the rival parties even in disagreement over whether a state of emergency exists.
A few hours before his term was due to end, Mr Lahoud issued a statement via a spokesman, Rafiq Shalala.
It said the army would have responsibility for maintaining order throughout the country.
Mr Siniora says he should take over temporarily under the constitution
"There are conditions and risks on the ground that could lead to a state of emergency," Mr Shalala said.
However, constitutionally Mr Lahoud could not call for a state of emergency without the backing of the government he did not recognise.
Mr Shalala said the army would "submit the measures it takes to the cabinet once there is one that is constitutional".
A spokesman for Mr Siniora told AFP news agency: "The statement issued by the general directorate of the president of the republic is not valid and is unconstitutional. It is as if the statement was never issued."
The head of the army has refused to comment. Gen Michel Suleiman was appointed by Mr Lahoud but has largely sought to keep the military neutral.
Our correspondent says there are reports that he has agreed to follow the cabinet's orders but that the situation may become clearer in the morning.
However, she says the one thing everyone does agrees on, at least for now, is that they do not want a return to violence.
Tension on streets
The election of a president requires a two-thirds majority, which means that the pro-Western ruling bloc - with only a slim majority - could not force its preferred candidate through parliament.
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, our correspondent says.
Checkpoints were set up and the ministry of interior suspended all firearm permits until further notice.
The crisis has raised fears of civil strife, including the possibility of rival administrations.
The issue has turned into a regional and international affair.
The US, Russia, Syria and Iran have all been 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.