Sussex Police are appealing for witnesses to come forward after a man died at the Big Church Festival on Friday.
The force said the man, who was in his 40s, died after a sign fell near the worship tent at about 3.30pm.
The South East Coast Ambulance Service NHS Foundation Trust said six patients were assessed and treated at the scene. Four were taken to a local hospital for further treatment, including two with more serious injuries and two with less serious injuries.
Six other people were injured in the incident. Police are asking anyone with information or video footage to report it online or call 101, quoting Operation Igloo.
The incident has sent shockwaves through the Christian community. The festival attracts around 40,000 people each year.
The Archbishop of Canterbury has released a statement expressing her sadness and shock, and offering prayers for those affected.
She said: "I pray for his family, friends and loved ones as they grieve. I pray for those receiving treatment, and the healthcare workers looking after them. And I pray too for the other festival-goers, staff and event organisers as they come to terms with these tragic events.
"May the God of comfort and healing be with them all."
Videos shared on social media show campers leaving the site after organisers asked everyone to leave by midday on Saturday.