The banking royal commission was dramatically interrupted on Thursday when a key witness, the head of Dover Financial Terry McMaster, collapsed while giving evidence.

Mr McMaster's collapse came after a strong exchange with counsel assisting Mark Costello where Mr Costello had accused Mr McMaster of giving a misleading answer and Commissioner Kenneth Hayne warning the the boss of one of Australia's biggest planning outfits that a key document was misleading and deceptive and thus in breach of the law.

But when Mr McMaster collapsed Commissioner Hayne quickly ceased the hearing, saying: "Adjourn and call an ambulance. Get an ambulance pronto. Move."

Shocked bankers, lawyers and staff from the Australian Securities and Investments Commission (one of whom was due to give evidence after Mr McMaster) filed out of the court room as Mr McMaster lay on the floor next to the witness box.