BANGKOK — A bomb exploded Monday within a central Bangkok shrine that is among the city’s most popular tourist spots, killing at least 18 people and injuring more than 100 across a hectic intersection surrounded by five-star hotels and upscale shopping malls.

With a powerful flash caught on security video and a boom heard blocks away, the blast from the improvised explosive device scattered body parts across Rachaprasong intersection, spattered blood, blasted windows and burned motorbikes to the metal. It exploded during evening rush hour as the area was filled with tourists, office workers and shoppers.

“Suddenly there was a big boom, and the whole room just shook, like someone dropped a wrecking ball on top of our ceiling,” said Pim Niyomwan, an English instructor working on the eighth floor of the building right next to the shrine. “The whole building just shook. My four students were hysterical.”

Video shortly after the blast depicts a scene of shock and desperation: people running for their lives and crying amid the debris; an emergency worker in an ambulance, frantically pounding the chest of a victim.

No one immediately claimed responsibility for the bombing.

“Those who have planted this bomb are cruel,” said national police Chief Somyot Poompummuang. “They aim to kill because everyone knows that at 7 p.m. the shrine is crowded with Thais and foreigners. Planting a bomb there means they want to see a lot of dead people.”

At least 18 people were confirmed dead and 117 injured, according to the Narinthorn emergency medical rescue center. The dead included Chinese and a Filipino, Somyot said.

As a single, devastating blow to this Southeast Asian metropolis, Monday’s bombing has no equal in recent history, though Thailand is no stranger to violent attacks. A more than decadelong insurgency by southern Muslim separatists has left more than 5,000 dead far from the capital. In Bangkok, politically charged riots centered on this very intersection in 2010 killed more than 90 people over two months.

Police said the bomb was made with a pipe wrapped in cloth. Police said it was too soon to determine the motive.

“We still don’t know for sure who did this and why,” Deputy Prime Minister Prawit Wongsuwon told reporters. “We are not sure if it is politically motivated, but they aim to harm our economy and we will hunt them down.”

The bomb detonated at Erawan Shrine, which is dedicated to the Hindu god Brahma, but is extremely popular among Thailand’s Buddhists as well as Chinese tourists. Although Thailand is predominantly Buddhist, it has enormous Hindu influence on its religious practices and language.

The shrine, adjacent to a five-star hotel, is at the intersection of two major arteries in the city. Throngs of tourists come there to pray at all hours, lighting incense and offering flowers purchased from rows of stalls set up on the sidewalk along the shrine.