The botulism scare has shaken international confidence in New Zealand's dairy exports which Fonterra, regulators and the Government are now scrambling to shore up.
Fonterra will conduct two internal inquiries into the incident, and the Ministry of Primary Industries yesterday gave details of its own probe into the way the problem was handled.
Mr Key had yesterday been expected to announce plans for either a ministerial inquiry or a commission of inquiry into the incident.
But he said a ministerial inquiry lacked the power to force witnesses to give evidence, and a commission of inquiry would take too long.
While it was favouring an inquiry under the new legislation, the Cabinet would make a final decision next Monday as to which form of inquiry it will run.
"Once these inquiries are complete I want to be able to travel to China and look down the barrel of their television cameras with the answers as to why this happened, give consumers confidence that it's been fixed and all issues have been identified."
United Future Leader Peter Dunne, who refused to give some information to the Henry inquiry into the leak of a GCSB report, said he recognised the need for a quick, thorough inquiry, but "what we've got to be careful of is that in resolving the Fonterra situation we don't unwittingly create problems for other inquiries that come along".
Labour deputy leader Grant Robertson said his party had supported the Inquiries Bill, but would have to consider any new amendments before supporting it further.
The four investigations
Government inquiry: To establish whether the scare was an isolated incident or indicative of a broader systemic issue.
Fonterra board-level inquiry: Led by independent director and former CBA and Air NZ chief executive Sir Ralph Norris to review the circumstances and principal decision points relating to the affected product, and look at Fonterra's business procedures, systems and practices.
Fonterra management-level inquiry: To find out why the incident happened, prevent it happening again, and ensure Fonterra maintains its "global leadership position within the dairy industry''
Ministry of Primary Industries "compliance investigation'': To determine whether regulatory requirements under the Food Act and the Animal Products Act were met by all parties, or whether any parties have committed breaches or offences.