More than 100 people are reported to be trapped in a bingo hall in Londonderry due to a security alert at Strand Road police station.
Speaking close to the scene on Monday evening, mayor John Boyle described the situation as “very worrying.”
Councillor Boyle said he hoped the situation would return to normal as soon as possible.
“I understand there are well over 100 people trapped in a bingo hall opposite the police station,” he told the BBC.
A PSNI spokeswoman urged motorists to avoid the area as a number of roads had been closed.