Four people are missing and dozens more injured after a Buddhist temple collapsed into a river in central Thailand on the first day of Lent today (July 16).

The wooden structure, Wat Phet Samut Worawihan in Samut Songkran collapsed into the Mekong River at around 1 pm.

Dozens of people were packed inside eating lunch on a national public holiday to mark the start of Buddhist Lent.

But the building could not stand the weight and after a loud ''cracking sound'', it slid down the muddy bank and crashed into the river.

Four people were dragged away by the current as dozens more scrambled for safety.

Rescue workers on the scene said that at least 20 people had been injured and taken to hospital.

While at least four others are still missing.

One local who was inside the building told local radio there was the ''sound of wood cracking'' before the building plunged into the water.

He then said there was ''splashing and screaming''.

Another witness Pink Maeklong said: ''Everybody was eating at the time inside the building. Then it just slid down into the water. Many people were still inside. They were screaming for help.''