The air ambulance has touched down in a playing field amid a huge police presence in a town centre. The aircraft landed in Gravesend, in a field off Trinity Road and close to Guru Nanak Darbar Gurdwara and Holy Trinity School. Reports have referred to someone in the area with a knife, but KentOnline is awaiting updates from police. In pictures taken from the scene by our reporter, at least seven police vehicles line the street. A cordon has also been set up in Khalsa Avenue, with an officer keeping guard. KentOnline reporter Keely Greenwood said: “A long stretch of road next to Guru Nanak temp…