A string of bomb attacks targeting Thailand's crucial tourism industry have killed four people.

Twin bombs exploded in the upscale resort of Hua Hin late on Thursday, killing one woman and wounding more than 20 others, including nine foreign tourists, and were followed by two more on Friday morning that killed another person and injured three.

A further two blasts struck on Friday in the popular tourist city of Phuket, reportedly injuring one person.

Two more bombs were reported in the southern provinces of Trang and Surat Thani, each of blast killed one person.