Police allege the group of masked males, aged between 13 and 18 years old, entered the grounds of St Laurence's College about 1pm and became involved in an altercation.

Two 15-year-old male St Laurence's students suffered knife wounds and were taken to the Mater Hospital for treatment. One boy was slashed on his left cheek and the other on his lower back.

One Year 11 St Laurence's student yesterday told brisbanetimes.com.au on the condition of anonymity that the first boy appeared to have had his face slashed open.

"One guy had to like hold up the other guy's cheek. It looked like the whole cheek was cut right open," the student said.

"Guys who saw it were shaking. It was so crazy."

The grandmother of the boy who was slashed in the face told ABC Radio he had undergone surgery and was today under sedation.

"His mother and father are not coping well at all,'' she said.

"They're quite traumatised as well.''

The alleged offenders will appear in Brisbane Magistrates Court this morning charged with one count each of grievous bodily harm and wounding.

Police said the males - aged 13, 14, 15, 18, and two aged 17 - are from suburbs on Brisbane's southside.

None of the boys were students at the school, police said.

Source: brisbanetimes.com