Police have warned people living near the railway line between Ballymena and Coleraine to beware of syringes which may have been thrown from a train.
Syringes may have been thrown from train
It follows an incident on Wednesday during which police seized four knives.
Police recovered them after reports that youths had been annoying other passengers. The youths were said to have knives, syringes and drugs.
The knives were seized at Ballymena, but no syringes were found and may have thrown out of the train.
The train stayed in Ballymena, and the passengers were taken on by bus to Belfast while officers searched it.
Police had first spoken to the youths while the train was in Coleraine.
"This morning police carried out a detailed search of the train, but so far the syringes reported by passengers have not been found, nor were any drugs recovered," a police spokesman said.
"As a precaution, in case the syringes were thrown from the moving train, we are asking people living or working along the line to be wary and to report to us any suspicious objects they come across."
He appealed for anyone who was on the train to contact police to tell them exactly what happened.