Hatyaiwittayalai secondary school in Songkhla will close its gates on Monday and Tuesday and provide online lessons after a sacked foreign teacher posted a firearm threat.

The school, which is on Phetkasem Road in Hat Yai district, has about 3,600 students and 250 teachers and staff.

School director Thitiwit Meechooworapong issued the closure order on Saturday night, saying the school would provide online teaching on Monday and Tuesday for the safety of its students and employees.

It follows a threat made by a “Mr Pieter Johannes Dreyer”, a former English-language teacher for English programme students at the school. 

On July 24 the school management terminated his employment for breach of contract. 

Afterwards, Mr Dreyer allegedly posted a picture with a firearm, messages and an audio clip in a public group on LINE chat, the school director wrote. The school management agreed the content amounted to a threat against the students, teachers and management.

The director wrote that the school management had filed a complaint with Hat Yai police.

According to police, the sacked teacher is a South African national. He left Thailand through the Padang Besar border checkpoint in Sadao district on July 19 and did not return.

The man allegedly posted a threatening message with photos of him firing a gun and photos of school executives in a school LINE chat room with about 5,000 users. He also criticised the school management.

Immigration police said he had already been blacklisted.

A screen capture of a message posted by LINE chat app user 'Kru Peter', together with a picture of a man at a shooting range.(photo supplied)