Detective Inspector Craig Bradley said:
"I am appealing for any people who were in the area and witnessed this incident, or the events leading up to this incident, to come forward and speak to my team.
"At this early stage it is unclear what the motive for this incident was.
"If you saw anything, or have any information which may help the investigation, please get in contact."
More top news
Nearly 1,500 people were evacuated from a central London nightclub, hotel and Charing Cross railway station after a major gas leak.
Princess Eugenie has become engaged to long-term boyfriend Jack Brooksbank, Buckingham Palace has announced.
Darren Osborne, 48, allegedly mowed down worshippers attending Ramadan night prayers in June last year.