Questions about Act policies provoked Jackson's Tuesday attack on Seymour.
"It's not about him being a useless Māori, it's about him being a dangerous politician actually," Jackson said today.
"He's a got a group of people who are trying to drive and support him," the Minister added.
"He's being aided by some of the right-wing commentators out there saying that he's talking for most New Zealanders. He's not. He's talking for about five or six per cent if he's lucky."
Jackson said Seymour should be challenged because agencies such as Ministry for Women, Ministry for Pacific Peoples, and Te Puni Kōkiri were very important.
"And we need to warn our people what's ahead: That this guy's going to disband some of the groups and agencies that have meant so much in terms of New Zealand development."
Jackson said despite Seymour's small support base, the Act leader could not be ignored because he was a potential coalition partner for National.
Seymour had already responded to Jackson's remarks by saying he was proud of all of his heritage.
"I'm not going to stoop to getting involved with someone like that. Willie Jackson, he's good for a laugh, but he's also a good example of why we need more serious people in charge of our Government and our country's future," the Act leader added.
"We shouldn't have ministries that are just there for a type of person, because every ministry should be serving every type of person."
Jackson's colleagues were asked about the remarks today.
"Willie has to be responsible for the statements that he's made," Deputy Prime Minister Grant Robertson said.
"Race relations is always a topic that people find challenging to discuss."
Kiri Allan, Labour MP for East Coast, said she had no time for personal attacks.
"Sometimes he minces his words," Allan said of Jackson.
"Perhaps he minced his words once or twice, but the point he is making is that he doesn't agree with the way that David advocates for Māori."
She said debates on issues such as co-governance were complex, and required a nuanced understanding of history.
"There's always a time for more maturity with respect to these discussions."
Allan praised former National Party Minister for Treaty of Waitangi Negotiations Chris Finlayson, who discussed co-governance on RNZ's The Detail programme.
Finlayson said the "sour right" was wallowing in racist, resentful rhetoric.
"They don't like tangata whenua. They dream of a world that never was and never could be," he added. "We've just got to leave those losers behind and move on."
