Video footage has emerged of a key suspect police want to question in connection with the deadly bomb blast in the Thai capital Bangkok.

The footage, from a CCTV camera, shows a man in a yellow shirt leaving a backpack in the Erawan Hindu shrine.

At least 20 people died in on Monday's explosion, including nine foreigners, and more than 120 were injured.

In a separate attack on Tuesday, an explosive device was thrown at a pier in Bangkok but no-one was hurt.

Authorities had already released still images of the man in the yellow shirt, who is wanted for questioning.

In the new footage, the suspect is shown carefully and deliberately removing his backpack inside the shrine, getting up without it and immediately leaving the scene.

The spot where he was sitting is precisely where the bomb went off a few minutes later, says the BBC's Jonathan Head in Bangkok.

"There is a suspect... we are looking for this guy," Prime Minister Prayuth Chan-ocha told reporters.

The bomb was detonated at about 19:00 local time (12:00 GMT) on Monday when the shrine, and the nearby Ratchaprasong junction, were crowded.

Prayuth called it the "worst ever attack" on Thailand.

"There have been minor bombs or just noise, but this time they aim for innocent lives. They want to destroy our economy, our tourism."

In a televised address that followed, he said the government would do all it could to bring the perpetrators to justice and told foreigners living in the country that it would try to safeguard them.

In Tuesday's incident, a device - possibly a grenade - appears to have been thrown at the busy Sathorn pier in Bangkok.

It landed in water where it exploded harmlessly, but police said it could have caused many casualties.

Monday's bomb was clearly placed to cause maximum casualties, says our correspondent in Bangkok.

In currency trading, the Thai baht fell to its lowest level in six years over concerns about the impact on tourism.

National police chief Somyot Poompummuang described the device as a 3kg pipe bomb - an improvised device where explosive material is put in a sealed cavity to maximise the explosive impact.

"Whoever planted this bomb is cruel and aimed to kill. Planting a bomb there means they want to see a lot of people dead," he said.

Marko Cunningham, a New Zealand paramedic working with a Bangkok ambulance service, said the scene was "like a meat market".

"There were bodies everywhere. Some were shredded. It was horrific," he told the Reuters news agency.

The shrine is dedicated to the Hindu god Brahma, but is also visited by thousands of Buddhists each day.

It sits between a five-star hotel and a popular shopping centre on the Ratchaprasong intersection, which has been the centre of political demonstrations in recent years.

Bangkok has seen a decade of sometimes violent rivalry between political factions.

The military took over the country in May last year, removing an elected government following months of unrest. The capital has been relatively calm since then.