Brownlee met with GNS Science chair Nicola Crauford today to discuss the matter.
Speaking to reporters this afternoon, he said it was now apparent that GNS had raised a 24-hour, seven-day-a-week monitoring system in various reports over the years.
"But they have never, ever provided anything directly to Government or even close to it."
Brownlee agrees that the public warning system will need to upgraded, given the inconsistency or total absence of warnings in some regions after the quake.
But it was irritating to face criticism "at a time when people were suffering", he said. A new warning system could not be "magic-ed up overnight".
GNS Science has estimated that a new warning system which sends messages to people's smartphones could be ready in 18 months - a timeframe which some say lacks urgency.
Brownlee said he wanted it in place as quickly as possible, but ruled out an immediate roll-out.
The Government wanted an advanced, smartphone-based system which was capable of tailoring warnings by region. Brownlee said overseas experience had shown that people became complacent if they were inundated with warnings.
Some commercial warning systems which were already available were unsuitable for New Zealand, he said. One option the Government had considered, called Tsunado, was "basically a box" which "screamed" warnings but could not tell homeowners about the location or scale of a tsunami.
The minister said he expected GNS Science's tsunami warning system to be at the heart of a review of emergency services' response to the quake.
Earlier today, Civil Defence director Sarah Stuart-Black said her agency would review its response to the quake "within weeks", once it had completed recovery efforts around Kaikoura.
It would be a broad-ranging review, but would have a particular focus on the problems experienced by regions in getting information about a potential tsunami.
"At this stage we know that there's a number of issues that have been raised about what happened locally.
"I don't have enough information on that, which is one of the reasons why we want to understand what happened around the country. That is a particular area I'm interested in as well."