A nurse sustained burn wounds after an unknown assailant allegedly threw a petrol bomb into the entrance of a grocery store in Pretoria’s northern suburbs.

Best Care emergency medical service said the incident occurred at the Les-Marais Spar in Paul Kruger Street on Wednesday afternoon.

“Best Care Emergency Medical Service attended an incident ... where a petrol bomb was allegedly thrown into the entrance of Spar, for an unknown reason and from an unknown person,” it said in a statement.

The petrol bomb caused an open fire which led to an elderly shopper sustaining first degree burns to her leg.

“The shopper [who is also a nurse] was treated on scene by Ambu-Link EMS and transported by Best Care EMS to a nearby private hospital,” read the statement.

Police are investigating the incident.

The Pretoria Record reported that the suspect allegedly “sped off” after throwing the petrol bomb.

“We thank our local SAPS for their fast response and we are grateful that no-one else got hurt. We pray for a speedy recovery for those involved,” said Best Care.