Police are concerned for the safety of a teenager and her baby son who have not been seen since an assault on a man at their caravan site.
Natalie Foster, 18, and seven-month-old Robert, have been missing since the "serious and violent" incident on Friday, North Yorkshire Police said.
A spokesman said a 43-year-old man was seriously assaulted at 5pm at the Seamer Caravan Site in Stokesley, where the mother and baby live.
Two men from Middlesbrough, aged 30 and 20, have been arrested in connection with the assault and remain in police custody.
Officers are trying to trace one other man, Mrs Foster's 22-year-old husband Robert, who is from the Southbank area of Middlesbrough.
Police said their primary concern is to ensure the safety of Mrs Foster and her child.
Her lack of contact with her family is "very much out of character and a great cause for concern", detectives said.
A spokesman said "extensive" inquiries were under way and all police forces in the country had been put on alert to assist in the search.
Detective Chief Inspector Kerrin Smith of North Yorkshire Police said: "As a matter of urgency, it is essential for the police to confirm that Natalie and baby Robert are safe and well.
"There has clearly been a serious and violent incident that has occurred near her home at Seamer Caravan Site in the Stokesley area at around teatime on Friday.
"There is no evidence at this time to suggest that Natalie or baby Robert have come to harm.
"However, the lack of contact from Natalie with her family in Trimdon, County Durham, since the incident, is very much out of character and a great cause for concern.
"To help put her loved ones' minds at rest, I urge Natalie to contact the police as soon as possible to confirm that both her and baby Robert are safe.
"I also urge Natalie's husband, Robert Foster, as well as his family and friends, to fully recognise the seriousness of the situation that has developed and to contact the police immediately."
Ms Foster is described as white with a fair complexion. She is 5ft 2ins tall, slim and has straight, dark brown, waist-length hair and green eyes.
Baby Robert is white with small features, straight blond hair with a red tint and blue eyes, police said.
Anyone with information is asked to call North Yorkshire Police on 0845 60 60 24 7 or Crimestoppers on 0800 555 111.