Cheng Li-wun, chairwoman of the Kuomintang (KMT), Taiwan's largest opposition party, is travelling at a time of increased Chinese military pressure on Taiwan, which Beijing views as its own territory, and as the opposition-dominated parliament stalls a government plan for $US40 billion ($A58 billion) in extra defence spending.
Speaking to reporters at her party's headquarters in Taipei before going to the airport, Cheng said she was going on a "historic journey for peace" but admitted some people felt uneasy about her trip.
"If you truly love Taiwan, you will seize even the slightest chance, every possible opportunity, to keep Taiwan from being ravaged by war," she said on Tuesday.
"So I would rather believe that all Taiwanese people hope this trip will succeed, because we can transform the most dangerous place in the world into the safest place in the world."
Cheng arrived at Shanghai's downtown Hongqiao airport under tightened security and then took a train to Nanjing, home to the mausoleum of party founder Sun Yat-sen who overthrew the last imperial government and founded the Republic of China in 1912.
China, which has never renounced the use of force to bring Taiwan under its control, refuses to speak to Lai, saying he is a "separatist".
Speaking in Taipei on Tuesday at a memorial ceremony for late democracy advocate Nylon Cheng, Lai reiterated his desire for equal talks with China.
"Equality and dignity are extremely important: Taiwan is not a part of the People's Republic of China and has the right to pursue a way of life that values democracy, freedom, and human rights," he said.
Late on Monday, Kuan Bi-ling, head of Taiwan's Ocean Affairs Council, which runs the coast guard, posted a picture on her Facebook account of Chinese warship deployments around the island - two off the east coast, and one each to the north, northwest and southwest.
"When you depart, you are doing so from within what they see as the 'Taiwan cage'," Kuan told reporters at parliament on Tuesday, referring to how China's military has termed Taiwan's planned T-Dome air defence system and talking about Cheng's trip.
Speaking separately at parliament, Taiwan's top official in charge of China policy, Mainland Affairs Council minister Chiu Chui-cheng, said Beijing should engage with Taiwan's democratically elected and legitimate government.
"We call on chairwoman Cheng Li-wun, when facing the Communist Party authorities in person, to demand that they immediately stop their compounded pressure against Taiwan, including military aircraft and naval harassment," he said.
Cheng is going to China a month before US President Donald Trump's scheduled summit with Xi in Beijing.
While Trump and Xi could strike goodwill agreements in Beijing on trade in agriculture and aircraft parts, they are also expected to discuss areas of deep tension such as Taiwan, where little progress is expected.
