A man jumped off the Dartford River Crossing on Wednesday evening just after 11pm and still hasn't been found.
Essex Police said officers were called by staff at the crossing to reports that a van had been left abandoned on the bridge.
A police spokesman said: "A review of CCTV showed someone jumping off the bridge into the River Thames a few minutes earlier.
"A police helicopter arrived to carry out an aerial search while HMS Coastguard searched the river.
"Met Police deployed their marine unit, to the section near east London but nothing was uncovered.
"The van was recovered and its owner was a man who lived in south east Essex.
"The bridge was closed for four hours while the incident was investigated."
The Gravesend RNLI lifeboat was called out to help look for the man on Wednesday night and Thursday morning to search.