An armed gang evaded a citizen's arrest as they sped away after a daring robbery of foreign students at a Mamelodi school in Tshwane.

A woman was shot in the arm, while a teacher suffered head injuries after being pistol-whipped by the criminals who robbed about 20 students yesterday.

The Viva Foundation of South Africa, an independent primary school in Alaska, an informal settlement, near Mamelodi East, was ambushed by armed robbers in a Toyota Quantum kombi during a visit by foreign students, mainly from the US.

An official at the school said she believed the criminals were trailing a bus carrying the students as they made their way to the facility.

According to employees at the institution who refused to be identified for fear for their safety, the foreign students arrived around midday in a scheduled visit.

However, when staff opened the gates to let them in, six criminals also went in undetected as they mingled with the students.

Once inside, they made the visiting students lay on the ground and robbed them at gunpoint.

"The next thing, as we came out of the building, the students were lying on the floor, the criminals were taking their bags which had their phones, purses, electronic devices and other personal belongings," one of the employees said.

A local teacher was also robbed and assaulted.

A smaller group of the visiting students had already made it into a Grade 1 classroom, where they were followed and robbed in front of pupils also at gunpoint, another staffer confirmed.

The students, attached to the University of Pretoria, make regular visits to the school which is situated in one of the most impoverished parts of the sprawling township.

"It happened so fast, maybe in eight minutes, they had taken everyone's bag and headed for the exit. We started screaming," the employee said.

When members of the community tried to stop the fleeing criminals, a woman was shot in the arm and had to be admitted in hospital.

Another woman, a local teacher, had to be hospitalised after being pistol-whipped by one of the criminals as they demanded her handbag.

Residents living near the school tried to stop one of the criminals as he got into a getaway minibus with no registration plates, eye-witnesses said.

"The foreign students were shaken, some of them were in tears with a few of them helping the injured," said the employee.

Police took an hour to respond, by that time, the criminals had disappeared into thin air, witnesses said.

"We are worried because we live next to the school as they target the school, we may find ourselves affected because they may run into our shacks when they escape," a resident said.

Staff members said this was the first criminal incident to happen at the school, which also houses a crèche.

Gauteng police spokesperson Capt Kay Makhubele confirmed the incident.

"We are investigating a case of armed robbery, we appeal to anyone with information to come forward. No arrests have been made so far," Makhubele said.

The visiting foreign students are studying courses that have elements of community work or teaching.