The curfew will also be in place in 23 provinces, officials say.
Bangkok remains tense after its first night under curfew and shots were heard early on Thursday near a temple where many protesters had sought shelter.
Some 27 buildings were set ablaze on Wednesday after protest leaders had surrendered.
Pockets of resistance still reportedly remain.
Some 40 people had died since troops ringed the protesters last week, with at least 14 more deaths on Wednesday.
Reuters news agency quoted a spokesman for Bangkok´s governor as saying there were 31 fires on Thursday morning.
There are fears that Central World, one of South-East Asia´s biggest shopping centres, could collapse after it was set ablaze by the protesters, Thai police officials were quoted as saying by AFP.
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