Highways England has said the outside lanes between between Junction 27 at Tiverton and Junction 28 at Cullompton Services are currently closed.
The Met Office has issued a yellow weather warning of snow and ice.
Heavy snow and rain in the area is quickly turning to ice on many road surfaces.
Shortly before midnight on New Year’s Eve, Highways England tweeted: “#M5 SB J27 #Tiverton to J28 #Cullomptom.
“Due to earlier snow fall we are currently in the process of deploying a snow plough.
“All lanes are running, however we have reduced speeds until the road surface has been made safe and the remaining snow cleared. Please drive carefully.”
At 2.21am, the service added: “The road still remains slippery in both directions, even after clearing the snow. We will shortly be gritting the road again.
“Please drive with caution.
But at 8.17am this morning, Highways England wrote: “#M5 J27 #Tiverton to J28 #Collumpton we currently have a Lane three closure in both directions due to earlier snow fall.
“We will shortly be gritting the road again.
“Please approach with caution and adhere to speed limits. Updates to follow.”
In the early hours of this morning Devon Live warned temperatures were dropping to as low as -7C overnight, urging drivers to take extra care on the roads.
The service wrote: “An extremely cold night across the county with road surface temperatures dropping to as low as minus seven degrees C on high routes.
“Our gritters have been out treating all night but drive with care and expect to find ice in places.”
Devon Live later twweeted: “We have a Yellow Weather Warning for Ice. Our gritters have been out throughout the night.
“Please take extra care and allow extra time for your journey.”
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