Four migrants were killed after being hit by a train while sleeping on the tracks in Greece, near the border with Turkey. (File photo)

Four migrants killed by a train in northern Greece may have been sleeping on the tracks when they were hit, authorities said.

The victims were two men and two women, aged 30-35, coroner Nikos Kifnidis told The Associated Press on Wednesday (Thursday NZ Time). He said they were lying down when the train hit and dismembered them, dragging their bodies for about 200 metres.

Blankets were found by the lines at the point of impact, suggesting that the migrants had wrapped up for sleep.

The tragedy occurred late on Monday (Tuesday NZT), near the land border with Turkey, which is a major entry point for migrants seeking a better life in Europe.

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It was only reported the next morning when a train driver saw the mangled human remains and called police. Initially, officials said three people had been killed, and their sex and age were unclear because of the condition of the remains.

They were hit near the village of Fylakas, between the northeastern towns of Alexandroupolis and Komotini. Officials said Turkish currency was found in one of the victims' pockets, suggesting he had recently entered Greece from Turkey.

Greece has seen a sharp increase in illegal immigration from the land border with Turkey, although most migrants still arrive on the eastern Aegean Sea islands in smuggling boats departing from the nearby Turkish coast. There has also been a rise in fatal road crashes involving migrants in northeastern Greece.

Police said on Wednesday (Thursday NZT) that a Syrian man was killed overnight and six more people injured when a car used by a smuggling gang that was crammed with nine people crashed on a northern highway near the town of Kavala.

A Syrian man and an Egyptian teenager were arrested on suspicion of human trafficking. The passengers were described as Syrian, Egyptian and Somali nationals.