Radio and television presenter Mike Puru remembered Magasiva as a "bloody good guy" who would always stop to talk to people.
The actor rose to fame on Shortland Street where he played nurse Vinnie Kruse-Miller from 2003-2006, and then returned from 2011-2018.
He also had roles in the Power Rangers television series, Sione's Wedding and Outrageous Fortune.
Olympian Dame Valerie Adams tweeted: "Rest In Peace Pua Magasiva. Thoughts and prayers to the family".
Magasiva co-hosted the breakfast show on Flava, a radio station owned by NZME, but left the show last year. NZME is the publisher of the Herald.
NZME chief executive Michael Boggs said: "It is with deep sadness that the NZME family has today been told of the sudden death of Pua Magasiva".
"At this incredibly difficult time our thoughts, prayers and condolences go to Pua's family, friends and his many colleagues.
"For us at NZME, Pua was a loved member of our radio team at Flava. We've been in touch with Pua's former workmates and are offering them support."
Workers from Flava wrote on Facebook: "RIP to our brother. Our Thoughts and prayers are with his whānau and friends".
R&B artist Vince Harder wrote: "No words uso, praying for your family at this time. Rest in love."
Also on Twitter Scotty Williams wrote: "Absolutely shocked by the news to hear of your passing brother. May your family find comfort at this time. Ia Manuia Lau Malaga... #RIP."
"My friend is gone," wrote Cassie Roma. "My heart is so, so sore. Please, if you need help, reach out. I know it's hard. We can all do hard things. Go well, Pua. Go well."
Mary Haddock-Staniland wrote: "RIP Pua, I'm speechless. You were such a delightful, caring, kind and beautiful character. Always had a spring in your step. Much love."
A South Pacific Pictures spokeswoman confirmed Magasiva's death and said she could not make any further comment.
Police confirmed they were called to a sudden death at an address in the Wellington central business district early this morning.
His brother Robbie was in Wellington along with other family members.
Magasiva, who has a young daughter from his first marriage, married Lizz Sadler in April last year, 18 months after meeting on Instagram. Sadler also has a daughter from a previous relationship.
Magasiva and Sadler travelled to Bali last month to celebrate their first wedding anniversary.
In 2015, he split up with his previous wife, Kourtney, whom he had married in 2012.
A police spokeswoman said there were no suspicious circumstances and the death would be referred to the Coroner.
Where to get help:
• Lifeline: 0800 543 354 (available 24/7)
• Suicide Crisis Helpline: 0508 828 865 (0508 TAUTOKO) (available 24/7)
• Youth services: (06) 3555 906
• Youthline: 0800 376 633
• Kidsline: 0800 543 754 (available 24/7)
• Whatsup: 0800 942 8787 (1pm to 11pm)
• The Word
• Depression helpline: 0800 111 757 (available 24/7)
• Rainbow Youth: (09) 376 4155
• CASPER Suicide Prevention
If it is an emergency and you feel like you or someone else is at risk, call 111.