Several foreign tourists were hurt in the latest blasts which followed a series of six coordinated explosions in other areas of central Bangkok that had killed two people and injured more than 20.
Hours earlier, authorities had cancelled the New Year countdown due to the six blasts and most people had left the area.
The last two explosions took place near the popular Central World Plaza mall where every year tens of thousands of Thais and foreigners gather for the New Year countdown.
One foreign tourist had to have his leg amputated.
A bomb scare also led to the evacuation of the Khao Sarn area, popular with Western backpacker tourists, half an hour after midnight.
As military personnel joined city police in search operations, authorities were still unable till this morning to identify the culprits.
While speculation has focused on southern Thai Islamic militants carrying out a violent separatist campaign for the past three years, political observers and analysts suspect the attacks to be the work of political elements to discredit the interim government installed after the September 19 coup.
Ousted Thai prime minister Thaksin Shinawatra's party last night said it had nothing to do with the Bangkok blasts.