Emergency services were called just before 10am.
St John said a patient had been taken to Whangārei Hospital via an ambulance.
A police spokesperson said one person was taken into custody but there was no wider risk to the public.
Law Society family law chairwoman Caroline Hickman said the attack was “horrendous” and “incredibly distressing”.
Hickman told RNZ barristers from around the country had been making contact today, sharing concerns.
“It makes family lawyers feel very vulnerable, because we’re already dealing with people in heightened emotional states. So it’s part of our role [is] that we do have to de-escalate people from conflict at times, but you certainly don’t expect to be physically attacked.
“It’s really unsettling for family lawyers to hear about.”
New Zealand needed “more family lawyers than ever, there’s a real shortage around the country - it’s because it’s a hard area of law to work in”, Hickman said.
“Family lawyers have chosen that area of work because they want to help people. And they want to help people who are at often the lowest point in their lives.
“So the people who are really in crisis, often, people who have heightened emotions, and if it’s about their kids, often, it’s incredibly sensitive, and for them an incredibly sad time.
“But it does mean that sometimes you’re dealing with people who are very volatile, and you have to work hard to try and help de-escalate things and calm things down.”
When asked if she had ever felt threatened in her work, Hickman said: “I’d be surprised if there was any family lawyer who hasn’t felt unnerved at times when dealing with someone in an acutely heightened emotional state, where they appear threatening or threatening towards you.
“Unfortunately, it’s something that does happen in our profession. And it can be extremely stressful.
“We don’t ever want this to happen again,” Hickman said, adding that lawyers she had spoken to agreed.
“We understand that the Ministry of Justice will be looking at reviewing the situation to see if there’s anything that they could be doing differently regarding the spaces.
“But we have security guards, we have searching when we go into courts ... We do appreciate that there is really good security checks at court. You go and you get screened.”
The court has reopened its doors and resumed hearings.
