Two persons have been rescued from the spot with serious injuries and admitted to Kottayam Medical College Hospital, police said.
The deceased were part of a six-member team of holidayers who had set out from Kottayam for Vagamon hill station on Tuesday evening.
According to local people, the accident happened close to midnight last night and the rescue work was delayed as the hilly tract had been enveloped by thick fog at that time.
On learning about the mishap, local people alerted police and fire force. The bodies were spotted and taken out in the wee hours.
The deceased were identified as Joseph George, Aneesh, Anto and Ratheesh, police said.