All power is back on at Britomart Train Station after they were disrupted by a helium balloon that entered Britomart Station and shorted overhead lines.

A tweet by Auckland Transport said services will resume departing from Britomart for all lines after a 45-minute delay.

The company thanked commuters for their patience and understanding.

An earlier tweet said four rail lines in Auckland were affected by the incident.

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The Southern and Western Line services were terminated at Newmarket Station, while Eastern Line services were ending at The Strand.

Onehunga customers were also affected, and were being asked to transfer to the Southern Line at Penrose.

An Auckland Transport spokesman said it wasn't exactly sure how the incident occurred.

"It happened at about 10.30am. Either someone brought a balloon into the station or one has floated down the tunnel," he said.

"Balloons are not allowed at any train stations for this exact reason."