Thai troops are locked in a tense confrontation with besieged protestors after three days of street battles in the capital that left at least 35 dead and 244 wounded.
Guests at a luxury hotel overlooking the sprawling protest site in the heart of Bangkok were forced to shelter in the basement after the building came under gunfire and was rattled by an explosion in the early hours of Monday morning.
Fire gutted three commercial buildings in another area.
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On Sunday, the government swiftly rejected an appeal by the "Red Shirt" protesters for UN-mediated talks.
A top protest leader also urged the revered king to intervene in the crisis.
The violence has turned parts of this city of 12 million people into no-go zones as troops use live ammunition against demonstrators, some of whom are themselves armed.
The Reds, whose vast base is under siege by troops, said they were ready to enter peace talks with the government immediately as long as the United Nations mediated.
"We want the UN because we don't trust we will receive justice from organisations in Thailand," protest leader Nattawut Saikuar said as the death toll from the urban warfare mounted.
The idea was rejected by the government, which has repeatedly warned foreign governments not to meddle in its affairs.
"No governments allow any organisations to intervene in their internal affairs," spokesman Panitan Wattanayagorn said.
Previous talks between the two sides have failed to reach an agreement, despite an offer -- since withdrawn -- by the embattled premier to hold November elections if the opposition demonstrators went home.
At the Dusit Thani hotel, which overlooks the Reds' encampment, guests rushed to the basement as staff warned them the hotel was under attack, according to an AFP journalist inside.
"I was in bed. There was a big explosion very close to my room. I went out of the room, other people did too and at that moment the wall outside was hit by bullets," AFP photographer Pedro Ugarte said by telephone.
It was unclear where the shooting came from.
Authorities said they would send workers from the Red Cross to help protesters -- particularly women, children and the elderly -- who wanted to leave the vast protest area by 3:00 pm (0800) Monday.
"Men can also leave the site but they have to show they are unarmed," army spokesman Colonel Sunsern Kaewkumnerd told reporters.
The army put off a plan to impose a curfew in parts of the city but did not rule out restricting night-time movements if the situation worsened.
Australia said it would close its embassy to visitors from Monday due to "ongoing violent clashes" including in front of the mission. The US and British embassies have already closed.
The government extended a state of emergency to five more provinces, ordered schools to stay shut Monday and declared two days of national holidays to keep civilians off the streets as they battled for control of the city.
Facing a military armed with assault rifles, the protesters have fought with homemade weapons including Molotov cocktails, fireworks and slingshots.
Some demonstrators have been seen with handguns and the authorities say grenades have also been fired by anti-government militants.
All of the fatalities in recent days have been civilians.
The Reds called on the king to intervene, saying he was the "only hope" for an end to the two-month-old crisis, which has left 63 people dead and about 1,700 wounded, including 25 fatalities in a failed army crackdown on April 10.
"I believe Thais will feel the same, that His Majesty is our only hope," Jatuporn Prompan told reporters at the rally site, where thousands of protesters were camped.
King Bhumibol Adulyadej chastised both the military and protest leaders during a 1992 uprising, effectively bringing the violence to an end, but has avoided commenting directly on the current crisis in public.
The Reds accuse Abhisit's government of being elitist and undemocratic because it came to power in a 2008 parliamentary vote after a court ruling ousted elected allies of their hero, former prime minister Thaksin Shinawatra.
Thai society is deeply divided between the urban elite and rural poor, with most of the Red Shirts from the north and impoverished northeast.
