Police were called to concerns for someone on the QEII bridge just before 5.20am today (Friday May 17).
Traffic was held while police officers dealt with the scene.
RNLI lifeboats from Gravesend were sent to the incident by HM Coastguard at 5.30am.
The bridge has since been opened but long delays remain in the area.
Further updates will be released as and when police receive them.
Samaritans is available for help 24 hours a day on 116 123.
A spokesperson for Essex Police said: “The bridge is now fully open. Thank you for your patience and understanding.
“We are currently on scene of an incident on the Dartford Crossing.
“We had been called to concerns for someone on the bridge shortly before 5.20am today (Friday 17 May) and have responded.
“This is an ongoing incident and traffic is currently being held.
“Please plan your route, we appreciate your understanding and will provide an update as soon as we are able to.”
A spokesperson for RNLI lifeboats said: “Gravesend RNLI Lifeboats were tasked by HM Coastguard to the incident at 5.30am.”
