Kent Police was called at 9.15pm on Sunday 18 July 2021 to a disturbance in London Road, near its junction with Fullers Hill.
During the incident, it is alleged a man in his 50s was assaulted by three people. He sustained a head injury and was conveyed to a London hospital where he remains in a critical condition.
Enquiries are continuing at the scene and a man and a teenage boy have been arrested on suspicion of assault.
Anyone with information is urged to contact Kent Police on 01622 604100, quoting crime reference 46/127385/21.
Investigators are also asking drivers with dashcam or residents with doorbell cameras to check for footage that may assist the investigation.
You can also call the independent charity Crimestoppers anonymously on 0800 555111 or complete an online form at www.crimestoppers-uk.org