The world watched transfixed as the first meeting between a sitting U.S. president and a North Korean head of state took place in Singapore on Tuesday (June 12).

People celebrate as they watch a TV showing U.S. President Donald Trump meets with North Korean leader Kim Jong Un during a news program at Seoul Railway Station. (Kyodo News via AP)

As crowds lined the streets of Singapore to see Donald Trump and Kim Jong Un head off for their meeting in the morning, millions more tuned in to watch the historic moment unfold "live".

The event was closely followed in the South Korean capital Seoul, where thousands gathered at railway stations and across various locations for public screenings of the landmark summit.

People watch live footage of the summit between U.S. President Donald Trump and North Korean leader Kim Jong Un in Singapore at a railway station in Seoul on Jun 12, 2018. (Photo: AFP/Jung Yeon-je)

Pedestrians look at a screen displaying live news of meeting between North Korean leader Kim Jong Un and U.S. President Donald Trump. (Photo: AFP/Martin Bureau)

Spontaneous applause broke out the moment Kim and Trump stepped out and greeted one another with a cordial handshake.

Giant screens at prominent buildings around Seoul also broadcast the meeting, with many stopping to soak in the momentous nature of the event.

A man watches television screens showing the summit between U.S. President Donald Trump and North Korean leader Kim Jong Un, at an electronics shopping centre in Seoul. (Photo: AFP/Yonhap)

South Korea's Yonhap news agency showed President Moon Jae-in smiling at the moment Trump and Kim shook hands.

"The North Korea-U.S. summit has now started," Yonhap quoted Moon as saying during a Cabinet meeting. "I guess the attention of all our people must currently be directed toward Singapore."

He added: "I spent a sleepless night. I, along with all our people, sincerely hope that it will be a successful summit that will open a new era of complete denuclearisation, peace and a new relationship between South Korea, North Korea and the United States."

South Korean President Moon Jae-in (R) and Prime Minister Lee Nak-yon (L) watch a television screen showing the summit between US President Donald Trump and North Korean leader Kim Jong Un. (Photo: AFP via Yonhap)

But there were also protests in Seoul, with anti-war activists rallying outside the U.S. embassy to call for peace treaty and an end to nearly 70 years of hostilities. The 1950-53 Korean War was concluded only with a truce, not a peace treaty.

South Korean activists march with banners reading "Make a peace treaty immediately!" during a rally demanding a peace treaty between North Korea and the U.S. near the U.S. embassy in Seoul on Jun 12, 2018. (Photo: Jung Yeon-je /AFP)

In Los Angeles' Koreatown, many gathered for communal screenings of the summit and cheered and clapped when images of the handshake beamed from Singapore.

Koreatown has one of the largest concentrations of Koreans in the U.S., and many residents there expressed their hope for a positive outcome in the lead-up to the Singapore summit.

People gathered for a U.S.-North Korea summit watch party in Koreatown, Los Angeles, clap as North Korea's leader Kim Jong Un shakes hands with US President Donald Trump at the start of their historic summit in Singapore, on Jun 11, 2018. (Photo: AFP/Robyn Beck)

On the U.S. east coast, crowds also took part in mass viewings of the event - with many gathered at New York's Times Square to watch the summit on TV screens.

People in Times Square walk past TV screens showing the meeting between U.S. President Donald Trump and North Korean Leader Kim Jong-un. (Photo: AFP)

In Tokyo, people rushed to get special editions of newspapers covering the summit as the Japanese closely watch the movements of Kim, who in the past has sent rockets flying over Japan.

A staff of a Japanese news paper Yomiuri distributes an extra edition of the newspaper reporting about the summit at Shimbashi Station in Tokyo. (AP Photo/Koji Sasahara)

Markets in Japan kept a close eye on proceedings in Singapore.

Japan's Nikkei share average rose on Tuesday morning, buoyed by optimism the summit could pave the way for denuclearisation of the Korean peninsula.

The Nikkei rose 0.5 per cent to 22,906.14 in midmorning trade, after dipping in negative territory briefly. The Nikkei was just a hair under its four-month high.

Employees of a foreign exchange trading company in Tokyo look at the screens displaying live news of meeting between North Korean leader Kim Jong Un and US President Donald Trump in Singapore, next to screen displaying the Japanese yen's exchange rate against the US dollar on Jun 12, 2018. (Photo: AFP/Kazuhiro Nogi)

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