Two horses were killed when the horsebox they were travelling in erupted in flames.
The blaze started in the vehicle travelling on the westbound carriageway of the M55 near to junction three at Blackpool, at 2pm on Saturday.
The horses were in the vehicle at the time.
Crews from Preston, Wesham and Fulwood fire stations attended the scene.
A spokesman for Lancashire Fire and Rescue said: “The crews put the fire out but the horses had already perished.
“As to what started the fire we’re yet to find out.”
The Highways Agency reported delays of up to 90 minutes while the incident was dealt with.
A spokesman for the Highways Agency said: “The horsebox was discovered to be well alight by the time services arrived with lots of smoke.
“All three lanes of the motorway were closed briefly at but this was quickly reduced to the two lanes by the police.”
The incident was further complicated by a broken down vehicle in the third lane of the motorway behind the fire.
All lanes were reopened by around 4pm.