Rescuers were scrambling on Tuesday to reach six people feared trapped after a bridge collapsed in Taiwan, smashing onto a group of fishing boats moored underneath.Dramatic CCTV images captured the moment the 140m long single-arch bridge came crashing down in Nanfangao, on Taiwan's east coast.In the images, the road gives way and tumbles down onto at least three fishing boats as a petrol tanker that was crossing also plunges into the water.The National Fire Agency said it believed six people were unaccounted for and could be trapped in the boats underneath the collapsed structure."The rescue operation is ongoing," the agency said in a statement, adding at least 12 people were injured, including six Philippine and three Indonesian fishing workers as well as the Taiwanese driver of the petrol tanker."We hope to safely rescue all in the shortest time to minimise the damage," Taiwan's President Tsai Ing-wen told reporters.The petrol tanker burst into flames at some point after it hit the water, sending a thick plume of black smoke into the air.It is not clear what caused the bridge, which was built in 1998 and spanned a small fishing port, to collapse.Taiwan was skirted by a typhoon on Monday night, which brought heavy rains and strong winds to parts of the east coast.But at the time of the bridge collapse the weather was fine.Taiwan has a huge fishing industry and many of those who work on its boats are low-paid migrant workers from countries such as the Philippines, Indonesia and Vietnam.Prosecutors have launched an investigation into the cause of incident, said transport minister Lin Chia-lung, adding that the bridge was still within its expected 50 year lifespan."Recent weather conditions, earthquakes and past assessments of the bridge will be taken into considerations. We will fully cooperate with the investigation," he told reporters.Previous serious bridge incidents in Taiwan have mostly been related to typhoons.In 2009, two bridges were badly damaged by Typhoon Morakot, which left more than 400 people dead.Taiwan, which lies near the junction of two tectonic plates, is also frequently jolted by earthquakes.The island's worst tremor in recent decades was a 7.6-magnitude quake in 1999 that killed around 2 400 people and destroyed tens of thousands of buildings.Although the devastating quake had ushered in stricter safety codes, several fatal incidents in recent years have triggered probes into shoddy construction.In 2018, a developer, an architect and a civil engineer were indicted over the partial collapse of a building that killed 14 people during an earthquake earlier that year.It followed a similar incident in 2016 when another quake killed 117 people - most in a single apartment block that collapsed.