Westfield Way was closed by police after a man fell from a bridge just after 4.20pm.
North Swindon Police said the road was closed from Purton Road to Haydonleigh Drive in both directions for 90 minutes "due to an ongoing medical incident".
Motorists were being advised to avoid the area.
Carrie Lee wrote on Facebook : "Air ambulance landed 5 minutes [ago]. Looked pretty serious, hope the guy is ok."
Lorraine Edginton wrote: "Thoughts with the person involved and to say what an amazing lot our emergency services are, especially the air ambulance which relies very heavily upon funding through organised charitable events in order to provide the amazing quick response service which does make a huge difference to those injured in getting them from the scene to the hospital."
Nicola Richards wrote: "Just saw air ambulance take off and I said a little prayer, this is awful, very sad."
Thamesdown Transport diverted its service 12 via Purton Road and Haydonleigh Drive during the closure.
UPDATE: Due to a Police incident Westfeild Way closed,service 12 diverted via Purton Rd, Haydonleigh Drive both ways.
— Thamesdown Transport (@thamesdown) October 8, 2015
- Westfield Way was reopened just after 5.30pm
- A man in his 20s is believed to be in a serious condition in Southmead Hospital's major trauma unit
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