A blessing is taking place at a Wellington Les Mills gym today after an instructor died while taking a class last night.

Tony Tuatoko, 40, died suddenly while taking a CX Worx class around 6.20pm, Les Mills Wellington spokeswoman Arpita Dutta said.

A Central Ambulance Communications spokesman said they were called to attend a "medical event" at the gym.

Mrs Dutta described Mr Tuatoko as one of the gym's "beloved" instructors.

"At this stage we don't know the details, but we are respecting the family's want for privacy.

"We're grieving ourselves, as well as the entire Les Mills family," Mrs Dutta said.

"We've closed down the studio today and there will be a blessing later on."

Mr Tuatoko is survived by his wife and three children.

On Mr Tuatoko's profile on the Les Mills website it says he has been involved with group fitness for the past six years.

"I love to workout out and I love to have fun at the same time," his profile says.

The gym advised of Mr Tuatoko's death with a post on the Les Mills Extreme's Facebook page saying: "Sadly, one of our beloved Group Fitness Instructors has passed away today. We will be mourning the loss so there will be no Group Fitness classes in Studio 1 on Saturday 24 January."

More than 80 people commented on the post.

"Such shocking and sad news," Lauren Donnellan wrote.

"Not many people could get me out of bed at 8am on a Saturday morning, but I loved Tony's combat class at Hutt City. Such a motivating and inspiring man, he will be missed by many. Thinking of his family and friends at this time x."

"We loved him," Katie Brown wrote. "Still can't get my head around the fact he won't be there for class next week."