The husband of a five-month pregnant woman who was killed in a hit-and-run on Sunday, has asked police to speed up their investigation and find the driver.

A black Volvo rear-ended a motorcycle driven by Thanayut Putpeng, 19, and ran over his pregnant wife, Nadeeyah Dechakamphu, 21, who was riding pillion.

Mr Thanayut told police the accident happened at around 10pm, as he and his wife were heading home.

He said he was driving slowly in the left-hand lane when he noticed a glaring headlight in his rear view mirrors.

Seconds later, the Volvo hit his motorcycle from behind, his wife fell onto the road, and the car sped off -- running over his wife in the process.

Residents and emergency workers rushed Nadeeyah to a hospital, where she and her unborn child were pronounced dead hours later.

Mr Thanayut said he was eager to hear about progress in the investigation, so he went to Min Buri police station for an update.

The superintendent of the station said CCTV footage showed that after the hit-and-run, the male suspect drove on for about 8km before abandoning the car and hailing a taxi.

Police found the vehicle had been sold by its owner in 2016, but the name on the registration document had not been updated.

The man who bought the car died in April, and his girlfriend had filed a police complaint claiming a friend of hers had borrowed the car but had refused to return it.