Thai authorities are looking for a suspect seen on CCTV footage as they investigate yesterday's deadly bomb blast in Bangkok. The bomb blast killed more than 20 people.

He was seen before with a backpack, and then later without one.

Police chief Somyot Poompanmuang says trace evidence was hard to find.

"This time, the attack was a 'perfect bombing'. There was no evidence left that could identify how the bomb was assembled, how it worked, even the residue from the bomb that could have been used to identify the type of the bomb wasn't available."

The government said the attack in the commercial centre was aimed at destroying the country's economy.

Thai Prime Minister Prayuth Chan-ocha promised the safety of foreigners in the country, and that authorities will track down those behind the attack. 

"In our country there are individuals or groups of individuals who are seeking to destroy the country. The ongoing attempts at destruction might be politically motivated, targetting the economy, tourism for whatever reason. The government will work to find those perpetrators and bring justice upon any networks involved as soon as possible."

The Erawan shrine sits on a busy corner near hotels and shopping centres and is a major attraction for tourists.