Outgoing Lebanese President Emile Lahoud has instructed the army to take control of security after the country's politicians failed to find a successor.
Mr Lahoud's presidency ends at midnight (2200 GMT). He said conditions existed that may lead to a state of emergency.
A vote for a new president failed after the pro-Syrian opposition did not allow the necessary quorum to be achieved.
The crisis has raised fears of civil strife, including the possibility of rival administrations.
Tension on streets
Mr Lahoud's spokesman, Rafiq Shalala, said the army would have responsibility for maintaining order throughout the country.
"There are conditions and risks on the ground that could lead to a state of emergency," Mr Shalala said.
Repeated attempts to elect a new president over the past two months have been scuppered by rivalry between the factions.
The election 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.
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.
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