Japan's second-oldest museum has raised $3.4 million through crowdfunding after reportedly being denied additional financial support to cover soaring utility bills to preserve its collection of animal and plant specimens.

More than 30,000 people have donated a total of 480 million yen to the National Museum of Nature and Science in Tokyo, easily surpassing the 100-million-yen target, campaign platform READYFOR said on Wednesday.

The head of the 146-year-old museum, Kenichi Shinoda, said in a video announcing the crowdfunding on Monday that they wanted to save the museum's collections, which he called "gifts from the past to the future".

He said that energy bills to keep some of its five million artefacts -- ranging from dinosaur bones to stuffed bears -- at constant temperatures and humidity levels were expected to almost double this fiscal year to more than $2.6 million dollars.

The cash-strapped Japanese government turned down the museum's request for more funding, and is even reducing its subsidies, according to media reports.

The museum in central Tokyo, which features a model of a blue whale outside, has previously turned to crowdfunding for three smaller projects, but the 100-million-yen goal was "the highest ever" for the institution, Shinoda said.

They have prepared unique gifts for donors in return, such as acrylic resin plant specimens, a museum tour by the president and a study session that allows participants to touch ancient human bones.

Shinoda said in the video that some people had advised him to lower the target, but it was reached in a matter of hours.

"Researchers and staff are touched to have received a great deal of support," the museum said on the campaign website.

The crowdfunding continues until November 5.