Gwent police say they are searching for a man, who's thought to have a knife in the Risca area.
It comes after an incident that happened just after 2pm at the car park of Risca train station.
Police were called after reports of a man with a knife threatening a man and a woman.
Both were left uninjured but distressed, following the incident.
Police are asking anyone with information about the incident to ring 101 or call crimestoppers anonymously.
Crowds have gathered in Risca today for a special parade and medal ceremony to honour the 203 (Welsh) Field Hospital's homecoming from a tour of duty in Afghanistan as part of Operation Herrick.
A teacher has been struck off for life for inviting schoolboys to his home to play cards then turning it into bondage games. French master Glyn Bevan, 55, asked the boys for card games - but then plied them with drinks to get them to tie him up.
A disciplinary hearing in Cardiff was told Mr Bevan kept gaffer tape and ropes hidden behind the settee at his home for his bondage "fetish".
The bachelor schoolmaster befriended teenage boy pupils during the mid 1990s at Risca Comprehensive school in Newport.
A disciplinary hearing of the General Teaching Council for Wales heard officers found dozens of framed polaroid photographs of Mr Bevan and the boys trussed up with rope and tape. Detectives identified 29 boys in the photographs and traced all but three of them.
One of his victims, identified as Pupil A, told police how he was indecently assaulted at Mr Bevan's home in the village of Rogerstone, near Newport.
Mr Bevan, who did not attend the hearing in Cardiff, resigned from the 500-pupil school in October last year. The disciplinary panel found him guilty of unacceptable professional conduct between September 1991 and December 2000.
A man arrested on suspicion of murdering Kyle Vaughan from Caerphilly in south Wales has been realised from police custody.
The 24-year-old was last seen at his home in Newbridge on December 30 and is now assumed dead.
A 27-year-old man, also from Newbridge, was arrested on Thursday and has been questioned by police since then.
Detectives have also released two other people on bail pending further inquiries -a man, 21, from Newbridge, and the boy, 15, from Abercarn, held on suspicion of assisting an offender.
Their release comes after a 62-year-old Newbridge man was arrested on Saturday on suspicion of perverting the course of justice and later released on bail.
Detectives are continuing to investigate Mr Vaughan's disappearance.
Police family liaison officers were providing support to the missing man's family after they were told last week he is now presumed dead.
They also appealed to the public for any information regarding Mr Vaughan's disappearance.
Concern had been rising for his welfare, as he suffers from diabetes and requires regular insulin injections, for some time.
A Gwent Police spokesperson said it is believed Kyle was last seen on the A467 between Risca and Crosskeys, "some time between 11pm and 11.45pm on December 30th 2012."
They added: "It is believed he was wearing a dark coloured beanie hat, a dark coloured t-shirt, three quarter length denim shorts, white trainers and a gold chain.
"On the same night at approximately 11.45pm, officers found Kyle's car, a silver Peugeot 306, which had been involved in a collision."
Specialist officers have been brought in as part of a major search operation focusing on several areas.
The missing man inquiry had been upgraded to a murder investigation on Friday after the arrest of the 27-year-old man on suspicion of murder.
But despite a nationwide police appeal and a growing online information campaign the whereabouts of the former Cwmcarn High School pupil remain a mystery.
Unilever worker Mr Vaughan is described as 5ft 8ins, of slim build, with short dark hair, and brown eyes.
He was known to wear a gold neck chain with a cross, has a distinctive tattoo of a pair of flaming dice on his inner left forearm and tattoos on his right leg.
Anyone with information should call 101 or Crimestoppers anonymously on 0800 555111.
A convicted killer hunted by police after he breached his licence conditions following his release has been been arrested.
37-year-old Jason Soal, who was released from prison in 2004, was tracked down in the Caerphilly County Borough area.
Gwent Police is appealing for information to find a convicted murderer who is being recalled to prison for breaching his licence conditions.
37-year-old Jason Soal was convicted at Cardiff Crown Court in 1992, but was released in 2004 on a life licence. Anyone who sees him is urged to contact Gwent Police.