Police are questioning students of a rival school seen travelling in a bus on Rama IV Road at the time.

Police detained 35 students of Bangkok Institute of Technology (BIS) after intercepting their bus at traffic lights near Khlong Toei shortly after the shooting.

A search of the bus discovered two pen guns, four knives and a number of partly consumed liquor bottles. A bullet hole was found in a left-side bus window.

Police said none of the students were cooperating. All had been tested for gunshot residue. The results were expected in a few days.

Khomkrit Raktham, 16, of Thaivijitsilp School of Art remains in intensive care.

He was hit in the head as he waited with 20 other students at a bus stop outside a Carrefour store.

Thong Lor police say witnesses heard a single gunshot as the bus drove by. The students ducked for cover but Khomkrit had already been shot.

A Thaivijitsilp student said he and some friends chased the bus, but halted when it stopped to let a group of young men off. They were allegedly carrying knives and fired two more shots.

A BIS lecturer said his school chartered buses to transport students. This helped minimise fights with rival schools.

He claimed superintendents checked for weapons before each journey.