"I know lots of people will be sending their love and support from in the Parliament and around NZ. The country will get in behind her. My love to her and her family."
Kaye was diagnosed with breast cancer in 2016, when she was in her mid-30s, and took leave from her ministerial roles to undergo treatment.
She dealt with the cancer privately, but spoke of the impact on her when she turned 40 in 2020.
Kaye left Parliament in 2020, and has kept a low profile since then.
Allan revealed this morning that she has been diagnosed with stage three cervical cancer, detailing how she had been suffering symptoms for months before her diagnosis and urging other women to get tested.
Prime Minister Jacinda Ardern led the outpouring of support, saying she was "gutted" by the news.
"It's fair to say, as a friend and a colleague, I've been gutted by the news - the whole team has.
"But we're also so heartened by the character, the person that Kiri is."
Ardern said that from the outset Allan had shown a "level of determination to focus on her health and wellbeing, but to ultimately come back and be a part of the team again".
Ardern said her focus now was to make sure she looked after herself first and foremost.
"And that we're here, really and waiting for when she's able to return."
The Prime Minister asked everyone to "look for the warning signs" when it came to cervical cancer.
National leader Judith Collins said Allan was "very brave".
"It must be an incredibly traumatic time for her and the fact that she had to deal with the Civil Defence issue while she knew this was all happening really does speak volumes about her dedication and courage."
Collins said the diagnosis was a reminder for all women to get a cervical smear test done.
"And it's also a reminder that this can strike people anywhere really, it's a very insidious disease.
"Kiri's situation is a reminder to every woman to get out there and get tested."
New Zealander of the Year Dr Siouxsie Wiles posted on Twitter, urging women to get checked "in honour of an incredible wahine".
Allan revealed that she found out about the cancer on the day she delivered her much-lauded message to the nation in the wake of the Kermadec earthquake and tsunami alert, which had many praising her bravery.
Rotorua's Tania Tapsell, the National candidate for the East Coast in last year's election, told the Rotorua Daily Post it was "devastating to see another strong woman battling cervical cancer".
"I have great respect for Kiri Allan and her work and have passed on our love and support to her," Tapsell said.
"This is a huge reminder for women to take on the urgent message from Kiri Allan and my cousin Talei Morrison and 'smear your mea'."
Labour MP Tamati Coffey posted on Facebook saying: "In Rotorua we know this story well.
"Cervical cancer is a threat to our women. Te Arawa legend, Talei Morrison fought the good fight raising awareness with women about the benefits of early intervention, before she passed.
"Today it's my colleague Kiri Allan who is about to fight the fight too. We as her work whānau are wrapping around her at this time as she faces one of life's big challenges.
"Mā te Atua koe manaaki e tiaki taku hoa."
Māori Party co-leader and MP for Waiariki Rawiri Waititi also took to Facebook to show his support.
"E te tuahine e Kiri Allan - Labour MP, kāore he kupu. You are so brave! And in the midst of internal turmoil you soldiered on and did the mahi!
"You are still doing it now. He wahine toa koe e te tuahine! I know you will beat this so I'm not going to get sappy with you but thank you for reminding us all how important it is that we encourage our wahine to #SmearYourMea.
"Tāne mā, Wahine mā encourage our wahine to get checked please, drag them to the doctors! Praying for you sister always. Now hurry up and get better so you can get back to stink Pōneke and do what you do best ... tiaki taiao, tiaki te iwi!"
"Fight of my life"
In a lengthy Facebook post, Allan told how long she has been experiencing symptoms as she faced up to the health battle.
"So now the fight of my life begins," she said.
"To be honest, I'm one of those gals that hates anything to do with 'down there'. And have taken a 'see no evil, hear no evil' type approach to that part of my body."
She said her last smear test was when cervical cancer campaigner Talei Morrison, just prior to death, rallied her whānau, her friends, the kapa haka community and ultimately NZ to campaign for women - and particularly Māori women - to get their smear tests done regularly.
"Talei's call to wāhine and whānau to get tested was the push I needed to get it done."
Allan said last year, during the election campaign, she noticed she was getting a lot of pain in her back, stomach and legs.
"I put it down to lots of driving, working long hours and the general stress of campaigns etc - so, I got my partner to give me a few mirimiri and forgot about it.
"Earlier this year, I realised I was finding it hard to sit for a lengthy period of time. Always in a bit of pain. I started running to try and move the lower back area a little bit. Nothing seemed to take the pain away."
Fellow MP urged her to see a doctor
She said that in late January, she started menstruating and didn't stop. She put off going to see a doctor, telling herself "that stuff usually sorts itself out".
But after four weeks, she said she went for a check-up at the GP, who put her on some medication.
"At about six weeks of menstruating with no change since the GP visit, I raised it with my colleague and friend Ayesha Verrall, who is a doctor, asking if the bleeding was a little odd.
"She asked a few more questions and I told her about the pain. She urged me, pleaded with me: 'Kiri, please, please, please prioritise this and go to the doctor tomorrow.'
"She made some recommendations and the next day I found myself having an ultrasound."
That ultrasound, she said, found a 3cm growth - she was told it was "probably benign".
"But the doctor made arrangements for me to go to the hospital the following day at the Women's Clinic. That day also happened to be the day of the tsunamis and earthquakes."
That day hospital tests revealed a 6cm tumour. Allan then immediately returned to the Beehive to front a nationally televised press conference on the latest tsunami warnings.
Prime Minister Jacinda Ardern confirmed this morning that Allan will undertake a leave of absence while she undergoes medical treatment.
Speaking to media, Ardern said she found it "remarkable" that Allan was leading NZ through a Civil Defence emergency while dealing with her diagnosis.
"If only people knew what else she was dealing with."
'Abnormal' result
"The following week I got a call saying the smears had shown an abnormal result and I needed to come in again for a colposcopy," Allan said.
She went for the procedure some days later.
"When the doctor was doing the colposcopy, she noted that there were abnormal cells showing and took another biopsy to test. She said the results would take a while, so I wasn't expecting any further news until a few weeks later."
Some days after that, Allan saw she had a missed call from her doctor, asking her to call back.
"I called back, going down the escalator stairs and the sound was rubbish. I skirted off to a corner to take the call properly, expecting good news.
"However, my kind doctor, who had been so incredible and taken calls from my family in the evenings, called to say the colposcopy had revealed I had cervical cancer."
Since then, she said her life has been a whirlwind of MRIs, CT PET scans, and preparing for chemo and radiotherapy, and any other therapy needed.
"The Boss, Jacinda, has been a mate, a colleague and my boss through this process. I cried telling her the night I found out. And her words were profound. I'll always have so much respect for the way she's dealt with me over these past couple of weeks or so. A text away - always.
"So today, she'll make an announcement that I'll be taking medical leave from work to focus on the fight I have ahead of me. She'll also be appointing acting ministers to my portfolios."
Allan said often, people's first questions is: "Is there anything I can do?"
"My answer now is yes. Please, please, please - encourage your sisters, your mothers, your daughters, your friends - please #SmearYourMea - it may save your life - and we need you right here."
