SHANGHAI -- China's tourism industry is seeing a speedy recovery as tourist attractions are receiving a surging number of visitors during the spring holidays.

Red tourism, which refers to visiting historical sites with a revolutionary legacy, was among the most popular types of tours during the Tomb Sweeping Day holiday, a holiday for people to mourn the deceased and honor martyrs.

According to data from Tongcheng-eLong, China's online travel agency, during the Tomb Sweeping Day holiday and the upcoming Labor Day holiday, the agency's flight bookings to red tourism destinations accounted for 15.6 percent of all flights, up four percentage points from the same period in 2019.

Shanghai, Beijing, Nanchang, Zunyi, Jinggangshan and Yan'an rank among the top 10 red tourism destinations, and 57.3 percent of visitors to such sites are aged between 20 and 39, according to Tongcheng-eLong.

Besides visits to revolutionary-themed tourist attractions, people also opted to pay their respects to the deceased and martyrs through online channels during the three-day holiday that ended on Monday.

On Tomb-sweeping Day which fell on April 4 this year, a total of 1,308 online memorial platforms received 3.78 million visits, the Ministry of Civil Affairs said. Meanwhile, on Twitter-like Weibo, "China has 20 million martyrs" is one of the trending topics, garnering about 270 million views.

In addition to red tourism, across the country, traveling and leisure activities such as rural tours and flower appreciation tours also gained popularity, according to OTA Lvmama.com.

New discoveries at Sanxingdui Ruins in Southwest China boosted visits to museums and sites with cultural relics. According to OTA Qunar.com, the overall popularity of cultural and historical sites across China during the holiday increased 3.8 times compared with 2019.

During the Tomb Sweeping Day holidays in 2019 and 2020, the number of domestic tourists was about 112 million and 43.3 million, respectively, according to data by the China Tourism Academy.

This year, as local cultural and tourism departments strived to enrich and increase their product offerings, it is estimated that 144.52 million domestic trips were made during the holiday in China.

According to a report by the China Tourism Academy, 4.1 billion domestic tourist trips are expected to be made in China in 2021, up 42 percent from 2020, and domestic tourism revenue is expected to surge 48 percent to reach 3.3 trillion yuan (about $503 billion).