TAIPEI, Dec 18 (Reuters) - Taiwanese were voting on Saturday in referendums that could affect ties with key supporter the United States as well as the island"s energy security, a vote the opposition hopes will be a show of no confidence in the government. The election comes as China has heaped pressure on democratic Taiwan to accept Beijing"s sovereignty claims and tensions between the two have soared. The main opposition party the Kuomintang, or KMT, was thrashed in presidential and parliamentary elections last year, failing to shake accusations from the ruling Democratic Progressive Party (DPP) and President Tsai Ing-wen that the KMT was too close to China. Of the four referendums, the two most contentious and high-profile ask whether to ban imports of pork containing the leanness-enhancing additive ractopamine, and whether to change the site of a planned liquefied natural gas (LNG) terminal to protect a reef. The government approved the pork imports last year, hoping to remove a stumbling block for a free trade deal with its most important international backer the United States, where ractopamine is widely used, and show it is reliable partner. It says the LNG terminal will secure the semiconductor-producing island"s energy supplies, and it will re-site the project further offshore to minimise the impact on the reef. The vote seeks a complete relocation. At a Friday night rally in central Taipei, KMT Chairman Eric Chu urged a yes vote to block ractopamine pork on safety grounds and move the LNG terminal, and sought to cast the vote more broadly. "There is no personal interest between individuals and parties, only the power of the whole people to fight back against the overbearing Tsai Ing-wen government," he said. A short distance away at the DPP"s rally near the presidential office, Tsai, referring to the pork issue, asked people to "understand the country"s situation". "Let the international community see Taiwan"s determination and be more willing to help Taiwan overcome China"s political interference and go out in the world." The KMT is also pushing for a "yes" vote in the third referendum, on restarting a mothballed nuclear plant, saying this is how to secure Taiwan"s energy security. The government is committed to phasing out nuclear power. Turnout is key. For a referendum to pass, at least 25% of the island"s roughly 20 million eligible voters need to vote in favour. So there must be at least about 5 million "yes" votes, and "yes" votes must exceed "no" votes. If the referendums fail, it would be a setback for the KMT ahead of mayoral elections late next year. Asked on Saturday whether the day"s cold weather could affect turnout, Chu said he was "of course worried".