Four passers-by were injured when an electrical transformer exploded in a huge fireball on a road in the Thai capital Bangkok.

The motorists were driving along Wireless Road when the electric device exploded near the Vanit Building in the city's Soi Phetchaburi 37 area at around 10:30 am on August 30.

Dashcam footage shows the moment the transformer blew up in a massive fireball, with a mushroom cloud of black smoke erupting from the site.

Firefighters extinguished the flames at 11:09 am, and traffic flow was back to normal, authorities said.

Police said four people were wounded, including Wichai Piromkit, a motorcycle taxi driver who suffered burns on his face and body when hit by the burning shrapnel.

He was rushed to the intensive care unit of the Theptarin Hospital, while the three other injured - identified by officials as Chaiyo, Thawatchai, and Chayakhom - were also receiving burn treatment at different hospitals.

Officers said four motorcycles and a taxi were damaged in the explosion.

The country's Metropolitan Electricity Authority (MEA) claimed the faulty transformer was used as a load break switch rather than a power supply. The affected equipment have been replaced, the agency said.

A spokesman said a MEA representative has visited the blast victims to provide financial compensation. They will also contact the owners of the affected vehicles to pay for the damages.

Thailand has one of the world's worst road safety records. Ministers have set the goal of reducing fatalities from 32.7 deaths per 100,000 people to 12 per 100,000 people by the year 2027.

However, a lack of road safety education in schools along with notoriously easy driving tests, police failures to enforce road laws, and chronic under-investment in infrastructure, all appear to hamper the efforts.