One person has been arrested.
He said in his opinion it was a terrorist attack.
Mr Corbyn said: "I am totally shocked at the incident at Finsbury Park tonight". Numerous victims are believed to have just left evening prayers after breaking the Ramadan fast.
"I tried to stop him (the suspect), some people were hitting him but I said stop him and keep him until the police came".
London's Counter Terrorism Command is leading the investigation into the attack.
"I will chair an emergency meeting later this morning".
The Muslim Welfare House released a statement calling for calm.
Numerous witnesses told CNN that they saw three men in the van, with two fleeing on foot after the other was apprehended.
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"There are a number of casualties being worked on at the scene", they added.
Witnesses reported seeing a white hire van veer off the road and into a group of pedestrians standing near a mosque just after midnight.
Mohammed Shafiq of the Ramadhan Foundation, a Muslim organisation which speaks out against extremism, said: "I utterly condemn the senseless and evil van attack against Muslim worshippers outside the Finsbury Park Mosque in London".
Opened in 1994, Finsbury Park Mosque is an unassuming five-story redbrick building in residential north London, close to Arsenal Football Club's Emirates Stadium.
"Some big van. crushing the people in the mosque".
The London Telegraph reported bystanders wrestled the van driver to the ground and pinned him down until police arrived. "There was three people in the van".
"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".
"I've seen about six or seven people on the floor". "He punched me in the head". And he just came into all of us.
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The mosque is near Seven Sisters Road and was once a notorious hub for radical Islamists but has entirely changed under new management. People were badly injured. "It's something we should not see".
"Our prayers are with the victims", they said on Twitter.
The mosque, which today operates largely as a community center, rose to worldwide notoriety in the early 2000s, due to its links with Egyptian-born radical cleric Abu Hamza al-Masri.
London Ambulance Service deputy director of operations Kevin Bate released a statement saying the most seriously injured people were the first to be taken to hospital.
The incident comes at a time when emotions are high in England, where there have been several recent terrorist attacks.
On May 22, a suicide bomber killed 22 people at a concert by American pop singer Ariana Grande in Manchester in northern England.
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