At least four people were killed and 15 others injured as multiple explosions struck Thai tourist towns, police said on Friday.
Two were killed on Thursday - one in the town of Hua Hin, one in Trang province and two others died in the second wave of attacks on Friday morning - one in Hua Hin, one in Surat Thani province, the Guardian reported.
At least eight explosions hit three cities in a span of 12 hours, police said.
The series of explosions started on Thursday night in the resort of Hua Hin. Two bombs placed near a local a bar called Johnny's 56 went off within a few minutes of each other as foreign tourists were leaving to go back to their hotels, CNN quoted Police Lieutenant Colonel Samoer Yoosumran as saying.
On Friday morning, six explosions occurred in three locations.
Two bombs went off Hua Hin, and the southern city of Surat Thani and the resort island of Phuket were each hit by twin blasts, police said.
The police said they have detained suspects but the group or motivation is still unclear, the Guardian added.
However, spokesman Piyapan Ping said the intention was to cause chaos.
Besides the bomb blasts, major fires were also reported in markets of several southern provinces, such as Nakhon Si Thammarat, Krabi and Trang, Xinhua news agency reported.
A lot of the places hit by blasts and fires, such as Hua Hin, Krabi, Phang Nga, are tourist hotspots famous around the world.
Thai Prime Minister Prayut Chan-o-cha said some Thais "without hearts" are making trouble, adding that the government will do its utmost to secure the kingdom.
Prayut also asked Thai people not to be scared by the series of bomb blasts.