Businesses and government offices in Bangkok are set to reopen on Monday after a week of disruption caused by anti-government red-shirt protests.
PM Abhisit Vejjajiva said the capital was "returning to normalcy", as residents staged a clean-up drive.
Thousands of people used wooden brooms and buckets of water to clear the streets, after violence which left more than 50 people dead.
However, a curfew in the city has been extended for two nights.
"Everything is calm and returning to normalcy," the prime minister said in his regular Sunday television address.
He said he would return to his office from the army base where he had moved during the protests, reports the AP news agency.
Mr Abhisit also defended the conduct of the security forces during their crackdown on anti-government protesters who had occupied parts of the capital for two months.
After the leaders of the red-shirts - named for the colour they adopted - surrendered, some protesters rampaged, setting fire to city centre shops and businesses.
Powerful hoses were used to clean up the debris, while electrical floor cleaners scrubbed the entrances to some shops to remove the black stains left from burning tyre barricades, reports the Reuters news agency.
The volunteers joined municipal workers to scrape off political posters and washed graffiti from walls and streets.
"I was shocked at first after seeing what the place has become, but then I felt pumped up after seeing a lot of Bangkok residents coming out to help," Wannaporn Sukhonpan, 40, wearing waterproof boots and a face mask, told AP.
Some of Bangkok's Skytrain services also reopened on Sunday.
The BBC's Karishma Vaswani, in Bangkok, says that while cleaning up the city is no easy task, healing the divisions in an entire society is far more challenging.
Most people here feel the country's problems are far from over, she says.
The red-shirts were demanding the resignation of Mr Abhisit, saying his government came to power illegitimately.
Mr Abhisit had previously offered to hold elections in November but withdrew the offer when the red-shirts refused to end their protest.
Many of the protesters in Bangkok came from the north and north-east of Thailand, where support for former Prime Minister Thaksin Shinawatra, ousted in a 2006 military coup, remains strong.