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Japanese Prime Minister Sanae Takaichi has vowed to use her dominance of Japan’s parliament following her landslide election victory to attempt to amend the country’s constitution for the first time in nearly 80 years.

Speaking on Monday night in his first press conference since his victory, Takaichi said his overwhelming mandate from voters left him feeling a “heavy, heavy responsibility to strengthen Japan”.

As part of that effort, he said his Liberal Democratic Party would now begin making arrangements to amend the constitution, which was drafted under the US occupation of Japan after the second world war.

“The constitution tells the story of the nation’s ideal form. With a keen eye on the future of this country, we will also advance the challenge towards constitutional reform,” said Takaichi.

Any successful effort to do so would represent a landmark in Japanese politics and one that has eluded many of Takaichi’s predecessors in the LDP, which was formed in 1955 with the central goal of trying to reform the constitution.

But constitutional changes require a two-thirds majority in the lower and upper houses of parliament, the National Diet, as well as a majority in a public referendum. No referendum has ever been held.

In Sunday’s snap election, Takaichi and the LDP’s coalition partner, the Japan Innovation Party, won 352 seats in the lower house, a so-called supermajority of more than two-thirds that puts the bloc in a starting position to clear obstacles to constitutional reform.

However, the LDP lacks even a simple majority in the upper house and will need negotiations with opposition parties to secure the necessary votes.

Takaichi did not specify which parts of the constitution he might seek to amend.

His pledge came as his victory in the snap election sent the Japanese stock market to a record high, as investors bet the government will implement an economic stimulus plan.

The Nikkei 225 closed up nearly 4 percent and the broader Topix rose 2.3 percent.

Past LDP leaders have often raised the possibility of changes, including giving the prime minister more power in a natural disaster or military crisis and lowering the bar on making future changes.

The most controversial are the proposals to change Article 9 of the constitution, which enshrines Japanese pacifism and states that “land, sea, and air forces, as well as other war potentials, cannot be maintained”.

Subsequent interpretations of that line allow for the existence of Japan’s Self-Defense Force, but constitutional change would give the military more political and practical legitimacy.

Takaichi also promised to push forward a controversial food consumption tax suspension for two years, contrary to some expectations that he would walk back the promise after bond investors worried it would overstretch Japan’s finances.

“We intend to continue … with discussions on setting the tax rate on consumption of food and beverages at zero,” he said. Seeking to ease market fears of borrowing to fund the tax cut, Takaichi said it would “not rely on special bond-financing bonds”.

Takaichi fought the election in the shadow of a row with China, from which he did not back down. At a press conference on Monday he reinforced his position by promising to seek further development of Shinzo Abe’s “free and open Indo-Pacific” regional policies.

Days after becoming prime minister in October, Takaichi answered questions in parliament about Japan’s response to a hypothetical Chinese invasion of Taiwan. His response – that such a scenario could be considered a “security threat” and could prompt Japan’s military mobilization – sparked an angry response from Beijing.

In response to Takaichi’s victory, Chinese foreign ministry spokesman Lin Jian said on Monday that the election revealed “some deep structural problems” and that the lessons of history should not be ignored.

Lin called on the Japanese government to “follow a path of peaceful development instead of following the path of militarism”.

The statement warned Japan that China unwavering in his determination to “defend the consequences of victory” in the second world war.

“If Japan’s far-right forces misjudge the situation and act carelessly, they will inevitably encounter resistance from the Japanese people and will be dealt a blow to the international community,” said Lin.