London police say one person is under arrest in an incident in which a vehicle collided with pedestrians. Police say there are a "number of casualties" at the scene and that emergency services are there. There's no word whether the incident is related to terrorism or if it's just an accident. However, it comes as Londoners are on edge following an attack earlier this month that left eight people dead. In that attack a van rammed pedestrians on London Bridge and then the three attackers began stabbing people at nearby Borough Market.