The 41-year-old was reportedly ‘crushed’ when the moped collided with the truck outside a 7-Eleven store in Thalang, central Phuket.
It was being ridden by her 29-year-old boyfriend, from Margate, Kent, who suffered only minor injuries.
The woman is from Blackpool and was six months pregnant, Lieutenant Colonel Sanit Nookong told the Phuket News.
She has been named only as ‘Sophie’ by local sources and her boyfriend as ‘Danny’.
Lt Col Nookong added: “They were not married, but they were partners and he was the father of her unborn child.
“Witnesses said the motorbike was travelling in the left lane northbound and pulled out to drive around a parked car, and was struck by the truck.”
The incident happened just after 12.10pm local time – 6.10am UK time – on Monday (08/05).
One witness said: “I just saw the end of what happened. A woman had been knocked off by a lorry and her boyfriend was really upset.
“They just took her away. I asked around and they said she was from Blackpool.”
It is believed the lorry driver, a 30-year-old local man, handed himself into police after initially fleeing the scene.