Lebanon is facing a potential power vacuum after its president left office with no elected successor, and rivals argue over who will now take control.
Before he walked out, pro-Syrian President Emile Lahoud said that the army should take charge.
But pro-Western PM Fouad Siniora says that under the constitution he and his cabinet are temporarily in power.
The crisis has raised fears of civil strife, including the possibility of rival administrations.
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, says the BBC's Kim Ghattas in Beirut.
KEY STEPS
Shortly before midnight on Friday, when his term officially came to an end, 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."
He refuses to recognise the government, and had said he would pass power to General Michel Suleiman.
The general has not said what he intends to do.
Political limbo
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.
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".
A few hours before his term was due to end, Mr Lahoud issued a statement via a spokesman, Rafiq Shalala.
"There are conditions and risks on the ground that could lead to a state of emergency," Mr Shalala said.
The BBC's Kim Ghattas 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.
However, constitutionally Mr Lahoud could not call for a state of emergency without the backing of the government he did not recognise.
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."
Our correspondent says the one thing everyone does agrees on, at least for now, is that they do not want a return to violence.
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