Ron Mark in hospital

New Zealand First MP Ron Mark is undergoing tests in Christchurch Hospital after suffering chest pains.

The Canterbury-based MP has been under intense pressure over the past few days after private details from his past became public in a row over whether information from his military files was being used by people connected to the Army to silence him.

Mr Mark's wife, Gail, released a statement through New Zealand First leader Winston Peters' office yesterday, saying her husband was in a comfortable condition.