The M3 northbound re-opens for a “safe, steady release of traffic” according to Hampshire Police.
Emergency services are also working “as fast as practically possible” to open the M3 southbound at junction 9 where delays are still over four hours on approach.
The road is expected to stay closed until at least 6pm this evening.
Police were called to the motorway at 3.49am due to reports of potential hazardous material.
They have been working with Hampshire Fire and Rescue Service and the Explosive Ordnance Disposal (EOD) team to clear material from the road.
No further details on the object has been given at this stage, but police say enquiries are continuing to assess what it is and how it got there.
More than an hour delay also continues on the A34 southbound towards M3 J9.
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