LONDON (REUTERS) - British bomb disposal experts were called to deal with a suspicious item found near a major bridge and tunnels spanning the River Thames near London on Friday after police arrested a man acting "unusually".

Kent Police said they had closed the Dartford Crossing, which carries traffic on the busy M25 London orbital motorway across the river to the east of the British capital, after reports a pedestrian was behaving strangely.

In a second operation linked to the Dartford incident, police said they had stopped a long-distance bus near the port of Dover, leading to the closure of the main A20 road, although this was later reopened.

"The Explosive Ordnance Disposal teams (EOD) are on the scene at the Dartford Crossing and are in the process of assessing the situation so appropriate action can be taken," police said in a statement.

Sky News said police had concluded the item did not pose a threat.

Motorist Graeme Brouder, 36, said he had seen the arrested man on the approach to the bridge.

"He came back towards the cars, he went across into the lane next to me, tried to get in the car next to me, he was shouting something," he was quoted as saying by the BBC.

"He was shouting at that car, tried to get in that car, ran past mine, tried my door handle, and then ran down the lane behind me and he was just shouting at everyone. He was running around, he was trying to get in everybody's cars."

The tunnel and bridge at Dartford, which carries some 165,000 vehicles on its busiest days, were closed in both directions at the height of rush hour as the police investigations were carried out.

Cargo trucks were stuck on the 2.9km bridge, which reaches 65m above the river at its highest point, while television pictures showed long traffic tailbacks as diversions were put in place.