Te Papa is marking 20 years in existence and major changes are on the way.

The national museum, on Wellington's waterfront, has had nearly 30 million visitors through its front door since opening on February 14, 1998. Two million people visited in the first year alone.

Te Papa chief executive Geraint Martin says the museum had discovered 400 new species, hosted more than 3000 powhiri, and rocked visitors with more than 1.3 million shakes of its famous earthquake house.

"Museums aren't cupboards full of old stuff, they're a mirror held up to society," he said.

"Our aim is that every New Zealander can see themselves reflected at Te Papa, and that international visitors can understand the richness and diversity of Aotearoa."

He says the museum has always faced criticism, and he hopes it always will.

"Given the significance of the stories we tell, it's very healthy that they are the basis for debate and disagreement.

"We are here to cherish and treasure our culture, but also to challenge the old ways of doing things, to engage and surprise, and sometimes to provoke."

Major changes are ahead for Te Papa in the coming years, Mr Martin said, including the opening of a new $8.4 million art gallery, Toi Art, next month, along with a new nature and environment area that will open in 2019.

"Te Papa will always be changing and offering new experiences, inside the building and beyond our walls," Mr Martin said.

Te Papa will mark 20 years with a special evening concert, and activities in the museum including special free tours and film screenings.

The museum will be open until 9pm on Wednesday.

TE PAPA FACTS:

• Busiest day was opening day, with 35,000 visitors
• Busiest year was 2015/16 financial year, with 1,784,939 visitors
• Gallipoli: The scale of our war was the most popular free exhibition, as 1.8 million visits were made from its opening on April 18, 2015, to the end of January this year
• The most popular paid exhibitions were Lord of the Rings (219,539 visitors from December 2002 to April 2003), Monet & the Impressionists (152,094 visitors from February to May 2009) and Whales Tohoroa (140,207 visitors from December 2007 to May 2008)
• Artworks treated by conservators: 1580
• New species discovered: 400+
• Scientific exhibitions: 700
• Children lost (and found): 3500
• Lightbulbs changed: 22,000

- NZ Newswire