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Traffic on the M25 was stopped due to concern for a woman.
Officers held vehicles travelling in both directions near Junction 1B at Dartford from about 7pm.
A police spokesman said: "Kent Police was called at 6.55pm on Saturday to a concern for the welfare of a woman seen on a bridge near The Brent, Dartford.
"Emergency services attended and road closures were put in place on the A282 and surrounding roads to ensure the safety of the woman and other road users.
"These road closures were lifted at 9.06pm and the woman was passed into the care of medical professionals."
The resulting queues stretched back to the Darenth Interchange at Swanley and across the QEII Bridge.
The A226 The Brent, in Dartford, was also closed in both directions between the Shell petrol station and the Brent Roundabout.
A National Highways spokesman confirmed the A282 near Dartford was closed in both directions between J1a and J2 "due to a Kent Police led incident".
There were delays of an hour between Junction 30 to Junction 1a clockwise and Junction 3 to Junction 2 anti-clockwise.
National Highways tweeted to say all lanes had been reopened.
Meanwhile, the police spokesman said officers were also called to a collision between two vehicles between Junction 4 and 5 of the M25 at 8.01pm today.