A fuel tanker that was being towed by a rescue truck broke free from the vehicle, ran backwards down a busy commuter road and jack-knifed – spilling up to 4,000 litres of unleaded petrol onto one of the main road routes through Cornwall.
The A38 remained partially closed for much of the day yesterday after the fuel tanker overturned and shed its load on Thursday night – causing major disruption for thousands of motorists which lasted into last night.
No-one was reported to have been injured in the incident.
The road was partially re-opened at 3.30pm yesterday for rush-hour traffic, but was closed again last night for re-surfacing.
A Devon and Cornwall Police spokesman said: "The consequences of this incident could have been far worse, and we are extremely fortunate that no-one was injured or killed.
"A motorcyclist could have been travelling behind, and if the accident had happened a mile sooner, the tanker could have crashed into houses.
"The incident has caused major disruption, due to the type of vehicle involved and the fact that it spilled a hazardous substance onto the road."
Police said the tanker was fully laden with 47,000 litres of fuel at the time of the crash.
A full investigation will be launched on Monday by the Health and safety Executive.
Breakdown crews were called to the scene after the fuel lorry broke down on at Menheniot at 4.30pm with reports that the vehicle's engine had blown.
Police were then called to the A38 near Tideford, between Saltash and Liskeard, shortly before 7pm after the tanker is thought to have detached from its tow and hit the road.
Thousands of litres of unleaded petrol is believed to have leaked from the fractured container as workers toiled through the night to prevent any major pollution to the River Tiddy, which runs through the village of Tideford, and connects with the Tamar.
Booms and absorbent pads were used in a bid to prevent fuel leaking into the river but there were fears some fish had been killed.
An Environment Agency spokesman said the road – which was still closed for a seven-mile stretch between Carkeel and Trerulefoot roundabouts for much of the day – was later expected to be resurfaced.
Environment Agency spokesman Steve Marks told the BBC: "If the petrol had got into the water it would have been a major environmental disaster."
As a precaution booms will remain in place over the weekend, but the agency said it was pleased a "serious incident" had been averted.