Massive ice release into Tasman Glacier lake at Aoraki/Mt Cook National Park

Massive icebergs have filled up at least a quarter of the meltwater lake at the foot of New Zealand's largest glacier, the Tasman.

The lake started to form in the late 1970s as the glacier rapidly retreated - fuelled largely by a warming climate - and it is now about 6km long.

Glacier watchers estimate the latest release of ice from the Tasman Glacier, the ice river that flows past Aoraki/Mt Cook, extends at least 1.5km.

More than three quarters of all the ice volume that existed in the Southern Alps at the end of the Little Ice Age in the mid-1800s had gone by 2016, glacier experts calculate.

But as well as saddening many mountain lovers, the Tasman lake and its icebergs thrill tourists who go out on the water in boats or look on from above the glaciers steep, rocky walls.

A guide, Richard Bottomley, posted an aerial photo of this week's release of ice from the Tasman.

"This is one of the biggest releases of ice from the Tasman terminal that I've seen," he said.

However, Glacier Kayaking owner and guide Charlie Hobbs said it was comparable to earlier releases.

"It's going to be awesome - it's giving us a lot of icebergs."