A vehicle hit pedestrians in London's Finsbury Park community, causing "a number of casualties", according to authorities.
One man died and eight people were taken to the hospital, Scotland Yard said.
A spokesperson for the Metropolitan Police said officers were called at 12.20am.
Eyewitnesses told British media that the van seemed to have veered and hit people intentionally.
"Over the past weeks and months, Muslims have endured many incidents of Islamophobia, and this is the most violent manifestation to date", it added.
Arsenal Football Club's Emirates Stadium is located close by, while further up Seven Sisters Road is the green space of Finsbury Park, which opened in 1869 and gives the area its name.
Britain's terrorist alert has been set at "severe" meaning an attack is highly likely. On May 22, a suicide bomber killed 22 people at a concert by American pop singer Ariana Grande in Manchester in northern England.
The incident comes after two deadly Islamist-inspired attacks this year that used vehicles to ram pedestrians - a stabbing spree earlier this month in the London Bridge area and a March attack in which a man drove a auto into crowds on Westminster Bridge.More news: Senate Democrat says any WH tapes due by Friday
The Muslim Council says a van has "run over worshippers" leaving the Finsbury Park mosque.
"We do not know how many were injured or killed, but our prayers are with the victims and families".
- How did Muslim groups react?
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. It is said that no radicalization happens here, but many have different belief as well.
Bergen added: "Ramadan, particularly in a country like the United Kingdom, where the days are very long in June, you know you're fasting from dawn to dusk and you're breaking the fast at night". The mosque, which today operates largely as a community center, rose to global notoriety in the early 2000s, due to its links with Egyptian-born radical cleric Abu Hamza al-Masri. However, in 2015, the mosque went for the revamp and the management was changed. Around 10% of the borough's population is Muslim.
"There was this white van stopped outside Finsbury Park mosque that seemed to have hit people who were coming out after prayers had finished". Vanzella said there have been no conflict among the groups in the past.
Transport for London says Seven Sisters Road has been closed northbound between Hornsey Road and Rock Street. Many police cars and ambulances were responding. "I saw everything. People were badly injured. They were helping on the pavement and trying to help them to get to the scene". Police said no other suspects at the scene have been identified or reported. The driver would undergo a mental health assessment in due course, police said. Ambulance crews said ten people had been transferred to hospital.