Five workers were killed and up to five others are feared dead after a motorway flyover bridge collapsed in Thailand in the early hours of Saturday morning.

The engineers were on top of the Rama 3-Dao Khanong Expressway - the scene of an almost identical accident that killed four last year - when an elevated bridge beam caved in at around 2 am on March 15.

Footage from the scene shows bodies buried under the mangled mass of concrete and metal along the Rama 2 Road in the Chom Thong District of Bangkok.

A cement truck driver who was present at the scene during the incident said concrete was being poured to connect the bridge pillars. He reported hearing a loud bang before witnessing the structure give way and crumble.

Five people have been confirmed dead, with another five still missing, authorities said. At least 27 people are reported to have sustained injuries.

More than 40 ambulances were dispatched to the site along with 200 officers. Officials said K9 units have been deployed to help search for trapped victims.

Police said the collapsed structure has disrupted the first-level expressway, a key route in the Bang Mot, Bang Khun Thian, and Chom Thong districts, which also serves as a major entry point to central Bangkok,

Officers said they are investigating the cause of the accident.

However, Thailand and other semi-developed countries in Southeast Asia have become notorious for their poor health and safety and frequent industrial accidents.

In November last year, on the same stretch of the expressway, four construction workers were killed when an under-construction part of the elevated motorway collapsed.

Local media reported 39 workers were on duty during the collapse. Twenty-five were safe, four were killed, and 10 were injured and sent to different hospitals.

A foreman present at the scene said several workers were buried under the collapsing concrete segments, while others were trapped under the crane.