Court closures will cut the connection between Northern Ireland's market towns and publicly visible justice, the Lord Chief Justice said.
Vulnerable people may have to travel long distances under proposals to shut eight courtrooms as part of budget reductions at the Department of Justice, head of the judiciary Sir Declan Morgan added.
He recognised scope for sharing public buildings, use of technology like Skype and speeding up justice but said remaining facilities should be "up to scratch".
"They involve the breaking of a connection between visible, active courts in market towns in Northern Ireland and the people who live there."
He added: "We will all need to rethink the way we deliver justice."
Almost £5 million has been spent in less than five years on eight Northern Ireland courthouses earmarked for closure, the Justice Department has disclosed.
Minister David Ford is proposing to shut Limavady, Strabane, Enniskillen, Magherafelt, Ballymena, Newtownards, Armagh and Lisburn in a bid to absorb an 11% - £2.3 million - annual funding cut to the NI Courts and Tribunals Service.
Sir Declan said closures needed to be handled carefully and pointed out that use of one Omagh courtroom could see defendants being brought through a public area from the cells.
He told Stormont's justice committee the level of new business coming into magistrates' courts had reduced by 23% due to increased police use of discretionary disposals for more minor offences which do not involve the formal justice system.
The head of the judiciary also said a pilot project in Newtownards had dramatically cut the amount of time cases took to come to court, producing cost savings, and added he planned to roll the scheme out across Northern Ireland.
But he warned remaining courthouses would come under more pressure following closures. The number of venues has fallen by 55% since 2013.
Sir Declan said Justice Minister David Ford had protected front line policing, prisons and probation services from the full impact of budget reductions.
"It is important to be clear about the fact that if these proposals are implemented in full it will change the shape of the delivery of criminal justice in Northern Ireland to the detriment of many vulnerable adults and children."
He added the department had a statutory duty to provide sufficient funding to allow access to justice and said enough time should be allowed to properly manage change.
"One of the unfortunate aspects of being caught in a squeeze like this is that the focus remains on what we can do this year or next year."
A pilot programme in Newtownards between the PSNI and Public Prosecution Service (PPS) allows guilty pleas to be made at the earliest opportunity.
The senior judge said: "The early results have been dramatic. The average number of days between a case reporting to a file being submitted is 75 days, under the pilot it was 29 days."
He said the number of court closures in Northern Ireland compared unfavourably with other jurisdictions.
"The proposals will certainly cause a strain on the remaining courts. I am not satisfied that there will be sufficient court space for all courts including the coroner's courts. Nor will all the courts be suitable."
He said that could make attending courts a very uncomfortable experience.
"Laganside court and tribunal users will have to travel greater distances to have the cases heard, with much greater numbers of court users attending and I have a concern that some of the waiting areas will be unable to cope."
He said little appetite had been displayed for using hearing centres more during evenings and weekends but said he was open to public institutions like councils using the buildings as long as they did not become politicised.
"I am conscious of the fact that courts are not the only public buildings, that there are different buildings operated by different departments, we may need to think about whether some use can be made of their facilities in order to ensure that justice can be properly delivered."
He said if court business was amalgamated hearings could begin later to allow people to travel there from outlying areas using public transport.
The Republic of Ireland had closed a large number of courts and built a smaller number of modern centralised facilities using private finance.
Sir Declan said: "There has been a realisation that we have to ensure that the quality of what we have left is up to scratch.
"If you decided this was the way forward, and that would be a decision for the department and this committee and others to think about, you would need to make sure that the rest of it was up to scratch."