A police spokeswoman said they received a report this morning of a firearms incident at the school, but at this stage it did not appear there was any danger to staff and students.
The report came in about 9.20am and the school went into lockdown of its own accord, she said.
"We've got staff at the school at the moment, obviously speaking with the informant. At this stage we don't believe there is any serious threat to anyone's safety."
Police were following up with the person who made the report.
Parents were notified at 10.12am that the school had come out of lockdown, and everyone on site was safe and unharmed.
It is the second time this week emergency action has had to be taken, after the school was plunged into lockdown on Tuesday after an alleged stabbing.
One person was arrested and another was taken to Wellington Hospital's ICU in a serious condition at the time.
One student had described the moment the school went into lockdown, saying they had been sitting in class when they were told "go to class, get on the ground, turn the lights off, shut the curtains".
The student, who did not want to be named, said they were in lockdown for about an hour, until 3.30pm.
In messages sent to parents on Wednesday, the school praised the "incredible" response from staff and students after the first lockdown.
"We know that our community will still be feeling the effects of [Tuesday's] events at the college, and we want to thank you for your support and understanding during this time," principal Andrew Savage said in the message.
"As this is an ongoing police matter we do not have any further information to share. Our thoughts are with those who have been impacted by the events."
Because the response from students and staff was so good, they would not be going ahead with a planned drill on Monday, Savage said.
"The safety and wellbeing of our students and staff is our priority and continues to be our focus."
He reminded students that when they came to Tawa College they agreed not to bring anything that could be used to harm themselves or others.
There would be guidance counsellors on site to support students, and supervised spaces are set up for students if they need a break.
"Extra security will be in place to support staff with supervision across the school grounds this week."
Savage asked that all students carry their ID with them - particularly Year 13s, who are not required to wear a uniform.
"It is normal to want to know what happened and so there may be lots of discussion."
The school has been contacted for comment on both lockdowns.
Parents earlier received a message from school with a copy of what the students had been told at form time on Thursday.
"When an incident happens it causes us to question what we stand for, what our values are, and who we are as a community," the message said.
"Tawa College is built on a strong foundation - on of justice that asks us to participate in our community with integrity, mercy, love, and service. This has not changed. What occurred on Tuesday is not a reflection of who we are or want to be.
"We all have pain and potential. It is our hope that you develop the ability to manage your pain without choosing violence or conflict as a solution."
The message urged students to consider each other carefully over the coming weeks.
"Each one of you is necessary. Each one of you is a part of our community. You all belong."
Students were told to say no to bullying and violence and offer opportunities for "restoration, mercy and change".
"Now is the time to stop simply talking about what we value, and start living it out with even more integrity than before."