A bomb has exploded outside a religious shrine in a bustling hub of the Thai capital, killing at least 21 people and injuring more than 120 others in an attack authorities said targeted foreigners.

The blast occurred about 6.30pm (2130 AEST) on Monday when the streetside Erawan Shrine close to upscale shopping malls was packed with worshippers and tourists. There are unconfirmed media reports that another bomb may have been defused.

Police confirmed 19 people were killed, including 10 Thais, one Chinese and one Filipino citizen. More than 120 others were injured, according to police.

The nationalities of the other people who died were not immediately clear.

“I heard a very loud bang, it made the whole building shake so I ran outside to see what had happened,” Panupan Chansing, 20, a hotel worker at the nearby Grand Hyatt Erawan, told AFP.

“I saw bodies lying on the ground and I saw vehicles on fire. I feel very sad and sorry that this has happened to Thai people … I’m scared.”

The attack is likely to raise concerns about the safety of tourists in the city – and the timing is particularly bad for Thailand’s travel industry.

The bomb exploded in the heart the city, at the Erawan Shrine, a popular attraction for both tourists and locals at the Ratchaprasong intersection in the busy Chidlom shopping district.

Several major hotel chains have branches in the vicinity, per Telegraph UK reports, including Holiday Inn, InterContinental, Renaissance and Grand Hyatt. Lumphini Park, Bangkok’s only bit of green space, lies a few blocks to the south.

Frances Geoghegan, currently in Bangkok and managing director of Cleveland Collection, a tour operator that offers packages to Thailand, said extra security had already been put in place at some of the city’s larger hotels.

Erawan Shrine is located directly next to the Grand Hyatt Erawan Hotel. The hotel said in a statement: “The safety and security of our guests, colleagues, and neighbors is a top priority. Following news of the explosion, Grand Hyatt Erawan Bangkok opened its doors to allow the public to seek refuge during this tragedy.

“Grand Hyatt Erawan Bangkok is working with authorities during their investigation and will look to see how the hotel can work with relief organizations as the situation unfolds.”

The Skywalk from the Hyatt, the Holiday Inn, the Intercontinental Hotel, and the Erewan Shopping District between the BTS (Skytrain) Chidlom and Siam stations will remain closed until Tuesday.

According to Australia’s Department of Foreign Affairs and Trade, Aussie travellers are being warned to exercise a high degree of caution, and in the regions of Yala, Pattani, Narathiwat and Songkhla, the Government has changed its travel advice to “Do not travel”.

Bangkok has endured years of deadly political violence, with a military junta now ruling the nation, and a decades-long Muslim insurgency in the far south that has claimed thousands of lives.

Police spokesman Prawut Thavornsiri told AFP the blast was likely politically motivated and designed to bring “chaos”.

Thailand’s defence minister said the bombing was aimed at foreigners in an attempt to damage the country’s tourist industry, which is a rare bright spot in an otherwise gloomy economy.

“It was a TNT bomb … the people who did it targeted foreigners and to damage tourism and the economy,” said Prawit Wongsuwong, a former general who is believed to have been one of the key coup-makers.

No one claimed responsibility for the attack, however, and it was unclear immediately who was responsible.

The Tourism Authority of Thailand (TAT) has urged tourists in the city to avoid the area and to remain vigilant travelling through busy parts of the city and report anything suspicious to police or security officers.

Flights currently are continuing to operate to and from the city as normal. According to TAT, all transport links in central Bangkok are running as usual but while the intersection is investigated there may be disruption to traffic.

Hotels and shopping malls in the surrounding area will be open as usual from today, while all other tourist attractions and services are open and operating as usual.

Islamic militants have carried out many attacks in other parts of Southeast Asia, including on Indonesia’s holiday island of Bali in 2002 that killed 202 people.

But they have not made Thailand a prime target.

A government spokesman said it was too early to speculate on who was behind the attack.

Glass was strewn across the street after the explosion inside the gates to the shrine, which is in the central Chidlom district close to the famous Sukhmuvit Road shopping strip.

Charred and shattered motorcycles littered the scene, alongside hunks of concrete, with pools of blood on the pavement and two bodies crumpled on the steps of the shrine.

The attack drew quick condemnation internationally, with UN Secretary-General Ban Ki-moon’s office releasing a statement saying he was shocked.

“He expresses his condolences to the bereaved families and to the people and government of Thailand,” the statement said.

“He hopes that those responsible will be brought to justice.”