STAFF from the north's agriculture department have returned to their posts conducting post-Brexit trade checks.
Inspections of animal-based food produce arriving at Belfast and Larne ports had been suspended amid concerns for the safety of staff.
One police car was parked outside the facility in Belfast Harbour.
One lorry arrived at around 1:45pm on a sailing from Cairnryan and was met by a Border Force officer.
Graffiti expressing opposition to a so-called Irish Sea border had appeared in the Larne area in Co Antrim.
Former Stormont agriculture minister Edwin Poots ordered the withdrawal of staff carrying out checks shortly before stepping down from the role to receive medical treatment.
His successor Gordon Lyons maintained the position.
The PSNI has since said there was no evidence of "credible threats".
Sinn Féin and the DUP are at loggerheads over whether the withdrawal of staff was justified.
Mid and East Antrim Alliance councillor Danny Donnelly said there had been "conflicting statements" in the aftermath of the withdrawal of port staff by the council and Department of Agriculture, Environment and Rural Affairs.
"I was surprised to hear a few days later the PSNI saying there was no credible threat," he told the BBC.
He said councillors feel they were not given enough information before the decision to withdraw the staff was made.
Alan Law from the union Nipsa said his colleagues have also been seeking answers.
"People need to be safe at their work and need to feel safe at their work... but we also need to know exactly what information these decisions were based on and those questions are still not being answered," he said.