Demonstrations are continuing for a second day in Beirut to try to force the Lebanese government to resign.
Protesters have promised to stay in Beirut until Mr Siniora resigns
Hundreds of protesters, including activists from Hezbollah and its pro-Syrian allies, are camped outside Prime Minister Fouad Siniora's offices.
Mr Siniora, who is there with his ministers, is refusing to step down.
The UK Foreign Secretary Margaret Beckett met Mr Siniora to express support for his government, rocked by resignations and a minister's murder.
The death or resignation of two more cabinet ministers would bring the government down.
Friday saw a mass protest in central Beirut, led by Hezbollah supporters who accuse Mr Siniora of being too pro-Western and anti-Syrian and of failing the Lebanese people.
Hundreds of demonstrators then stayed to pitch tents on streets leading to the government's headquarters.
The BBC's Jon Leyne says it was the first of what could be many long nights as the demonstrators have vowed to stay until Mr Siniora's government resigns.
It is all very similar to the protests that brought Mr Siniora to power 18 months ago and curtailed Syrian influence in Lebanon, our correspondent says.
The demonstrators brought water pipes, small radios and even musical instruments for entertainment.
Moments after waking on Saturday morning, they resumed chanting slogans against Mr Siniora and his government.
"We will stay here until the fall of the government which is under the tutelage of the United States," one protester, Nadia Assaf, told the French news agency, AFP.
"We do not want any tutelage over Lebanon, not Syrian, not Iranian, not Western."
Soldiers cordoned off the government office complex with barbed wire and armoured vehicles.
UK Foreign Secretary Beckett said she supported the government
Mr Siniora has said he will not be forced from office by mass protests and has vowed to stand firm against what he has called an attempted coup.
He met Mrs Beckett on Saturday, who later told journalists that the Lebanese government was obviously facing difficulties.
"It has shown considerable courage and steadfastness in the face of very serious problems," Mrs Beckett said.
"This is a government elected by the people of Lebanon and which has the constitutional authority an election gives it."
The US has denounced what it described as "threats of intimidation violence" in Lebanon.
A State Department spokesman, Tom Casey, accused Syria and Iran of instigating the protests which he said were aimed at toppling the democratically-elected government.
US Ambassador to the UN John Bolton called the Hezbollah demonstration "part of the Iran-Syria inspired coup".
The opposition, which involves a number of groups, has promised to carry out more surprise moves to bring down the cabinet.
A Hezbollah member of parliament Ali Ammar said: "We won't leave these squares until this authority complies with the will of the majority of the people - most of whom want to escape this crisis and form a unity government."
Hezbollah has been demanding a bigger share in the cabinet that would give it the power to veto government decisions.
The government came to office last year in the first election held after the withdrawal of Syrian troops originally stationed in Lebanon during the civil war.
Syria was forced to withdraw its military presence after massive street protests and international pressure, triggered by the February 2005 assassination of former Lebanese Prime Minister Rafik Hariri.
A UN investigation has implicated several Syrian officials in the killing, although Syria has denied any involvement.
The government in Beirut has also accused Damascus of ordering the assassination on 21 November of anti-Syrian cabinet minister Pierre Gemayel.