Police believe missing baby 'has come to serious harm' as hundreds of officers continue search
WATCH: The latest update from Sussex Police and the Metropolitan Police
Police believe a missing two-month-old baby "has come to serious harm" in Sussex.
That's according to Metropolitan Police Detective Superintendent Lewis Basford and Sussex Police Chief Superintendent James Collis, who spoke to the media on Wednesday afternoon.
The officers revealed that the search, involving hundreds of personnel, police dogs and drones, has now been extended to 90 square miles.
Constance Marten and her partner Mark Gordon were arrested on suspicion of child neglect on Monday night, after more than 50 days on the run.
The pair have since been further arrested on suspicion of gross negligence manslaughter.
The couple remain in police custody after the police asked for an extension, to give them more time to question them.
In a statement, Detective Superintendent Lewis Basford said: "I can confirm that Constance Martin and Mark Gordon remain in custody after an application for the extension of their detention for a further 36 hours has been sought from Brighton Magistrates’ Court.
"The police searches for the baby continue; we must consider that the baby has come to serious harm.
"Detectives from the Met’s Specialist Crime Command are now leading enquiries to locate the baby because of the resources, technology and expertise available to them in very complex investigations.
"This is a hugely difficult and painstaking search operation covering a vast area of some 90 square miles.
"We are using every resource we have at our disposal to find the baby; the police helicopter, sniffer dogs, thermal imaging cameras and drones are being used to assist Met and Sussex Police officers who have worked through the night into today.
"Specifically we have conducted searches in Newhaven and open areas to the east and north of Brighton including the South Downs.
"Members of the public can expect to see search teams working over the next few days.
"Support from the public has been vital during the course of the investigation so far and will continue to be.
"I would reiterate that members of the public can help us by remaining vigilant, and reporting any suspicious behaviour or items found in their gardens, outbuildings and sheds, between 8 January and Constance and Mark's arrest.
"Equally if you are out walking in these areas and you discover something you think we should know about, please don’t hesitate to contact us, no matter how insignificant it may seem.
"Before their arrest, the last known sighting of Constance and Mark was in Newhaven on Wednesday, 8 January.
"I'm therefore reiterating the appeal to members of the public between Brighton and Newhaven to report any potential sightings, or information about where they may have been sleeping, to the investigation team.
"Anyone with any sightings or information that could assist the search is asked to call the Met police incident room on 0208 3453 865 or 999 with anything they believe may be significant."
WATCH: Police carry out searches for the missing baby at an allotment site
Police officers have been scouring a park and golf course near where the couple were found.
Searches for the baby have also been carried out at Roedale Valley Allotments, along with door-to-door enquiries.
Drones and helicopters were deployed on Tuesday (28 February) to help officers on the ground with locating the child.
Police said Marten, 35, and Gordon, 48, were living outdoors before they were found.
The couple had been spotted by a member of the public at a convenience store shortly before 9.30pm on Monday (27 February).
They were then arrested by officers from Sussex Police in Stanmer Villas, Brighton within six minutes of getting a 999 call.
It is unknown if their baby was full-term or has any health issues.