Passing through six heavily-guarded gates underground, 100 lucky visitors got the chance to have a close look at the most secret part of Nanjing Museum on May 17.

The itinerary included two warehouses holding paintings, calligraphy and metal articles, plus rooms used for cleaning, restoring and photographing cultural relics.

The visitors won the one-hour free tour online.

According to Tian Mingli, director of the collection management department at the museum, it is the first time the museum has opened this part of its collection to the public in its 81-year history.

Home to about 420,000 cultural relics, Nanjing Museum has one of the country's largest collections.

Though the museum's exhibitions rotate every one to two months, only 40,000 pieces can be on display at a time.

"This might have ignited the public's huge curiosity to see what the rest are like," Tian said.

Normally, only professional teams are allowed into the warehouse with the signature of the museum curator. Keys and codes unlocking each warehouse are preserved by two departments and will only work when used together. Tian said the level of security is even higher than banks.

For tourists, no cameras, cell phones or even pens are allowed into the maze-like warehouse.

Ma Minda, a power engineer, was one of the visitors.

"As a fan of cultural relics, I'm really excited to see them in the warehouse," he said.

"I would love to see more stored items be exhibited in the future, allowing people to know more about our history."

Zheng Jing, who is in charge of the social service department of the museum, said their website was flooded with applications.

"To ensure the safety of the relics, we cannot allow too many visitors in this first trial," Zheng said.

"Possibly, we will have similar events more often in the future and explore more ways to accept applications other than the website to give more chances to kids and older people," said curator Gong Liang. "However, it's still too early to have a detailed plan."

The event also marked International Museum Day, which falls on Sunday. As China's main venue of this year's celebration, Nanjing Museum also launched a series of special exhibitions through this weekend.