Dozens of people had just finished prayers at the mosque when the vehicle crashed into pedestrians in Seven Sisters Road at about 12.15am on Monday.
One man has been arrested and the Metropolitan Police confirmed that one man died and that Counter Terrorism officers are investigating the attack.
Witnesses said people were also attacked by a knife-wielding man but the Met said there had been no reports of anyone suffering stab wounds.
At this stage there are no reports of any persons having suffered any knife injuries.
The driver of the van – a man aged 48 – was found detained by members of public at the scene and then arrested by police in connection with the incident.
He has been taken to hospital as a precaution, and will be taken into custody once discharged. He will also be subject of a mental health assessment in due course.
A number police units are at, and managing the cordons around, the crime scene, including local officers and those from neighbouring boroughs – supported by armed officers and the Territorial Support Group.
The investigation of the incident is being carried out by the Counter Terrorism Command.