The alert said trains are delayed across the network.
An Auckland Transport spokesman said the trains were being stopped “near the station until we have clearance to reopen the building”.
“We expect there will be delays and cancellations to trains throughout the morning as a result.
“We’re asking customers for their patience and to check the AT mobile app for the latest information about train services and alternative public transport options.
“When we are able to run trains from [Britomart] Station again our train crews will work to get services back running to timetable as soon as possible.”
Sign up to The Daily H, a free newsletter curated by our editors and delivered straight to your inbox every weekday.