SINGAPORE — Government officials here surprised United States president Donald Trump with a 2kg birthday cake, but they were the ones who were later caught flat-footed when a last-minute request came in from North Korean leader Kim Jong-un to tour the city.

The historic United States-North Korea summit on Tuesday (June 12) may have been brief, but it was not short on surprises.

When Mr Kim decided to head out to sightsee on the eve of the summit, public servants had just a "few hours" to prepare for it because they had not anticipated it.

Mr Ong Siew Gay, chief of protocol at the Ministry of Foreign Affairs (MFA), told TODAY: "I think for this, our assumption was that because they were preparing for the summit the next day, there would be no other elements.

"(Mr Kim) asked to go on some site visits on Monday evening. This was at their request, we didn't offer it."

Mr Ong, who joined MFA in 1995, called it "a very challenging evening", but also "very exciting".

Photo: Najeer Yusof/TODAY

"We had to work with the Traffic Police, they had to close the roads… decide the best route to take (to the different locations), and of course (we were) also scrambling to call our colleagues in the Ministry of Communications and Information," he said, referring to arrangements to inform and take care of the Singapore and international media.

The North Korean leader later went on an excursion around Gardens by the Bay and visited the skypark of integrated casino resort Marina Bay Sands, before ending his roughly two-hour-long tour with a walk around the Esplanade promenade.

To prepare and execute this unprecedented event on short notice, about 80 MFA officers from the policy, strategic communications and protocol divisions were involved. They were supported by those from a few other ministries, including home affairs, education and transport.

Not just the delegations from US and the North Korea, but about 2,500 reporters from around the world were here. Some S$20 million had to be spent on security and logistical needs, and at least 5,000 Home Team officers, including police and Singapore Civil Defence Force officers, were deployed.

The lead-up to the summit, which saw some twists and turns, was unexpectedly confirmed on June 1, a week after Mr Trump had called it off. The two leaders had been on hostile terms over North Korea's nuclear and missile programme, but in the first surprise of many, they both agreed to finally meet for the first time in Singapore, arriving on June 10.

Mr Kim, who arrived first, called on Prime Minister Lee Hsien Loong at the Istana shortly after, and Mr Trump touched down that same night.

PM Lee then met the American president and his delegation the next day for a working lunch.

A highlight at the lunch was a "surprise" early birthday celebration for Mr Trump (who turned 72 on June 14).

The MFA team, which oversaw matters such as the two visiting leader's motorcade arrangements and key activities at the Istana comprising meetings with PM Lee, had to check with the US side beforehand about the birthday plan.

"In our team… we like to engineer surprises," Mr Ong said, adding that those working on the ground "all knew what was going on".

As for whether guests were surprised by the gesture, Mr Ong said: "You have to check with them to see if they were indeed surprised, we couldn't tell."

Mr Trump was offered what appeared to be a gilded fruit cake during the lunch. The organisers did not delve into the details, only saying that the cake weighed "2kg to 3kg" and had a "golden-coloured candle".

Ms Jessica Tan, a protocol officer at MFA, said: "We had to make sure (the amount of cake) was sufficient for the lunch guests, and also not too tall because it will be very heavy for the butler carrying it."

Asked if it was a norm to celebrate birthdays of other heads of states, Mr Ong said: "We try to show a certain personal touch. Sometimes, it happens to be the leader's birthday. Sometimes, it could be other things."

For example, if other heads of states were visiting with their spouses, they (the spouses) could be taken on a tour around the Istana gardens if they are interested in horticulture.

Apart from the cake, Ms Tan spent "sleepless nights" over the main meal, researching Mr Trump's dietary requirements and his preferences for chocolate cake and vanilla ice-cream, for instance, and then checking them with the US delegation.

Conflicting media reports about the American president's preferred protein added to the challenge of locking down the menu in less than two weeks.

Mr Ong said: "(There were) recent reports that said Mr Trump had switched from beef to fish, so we had to check."

The final selection included dishes such as lobster bisque, angus beef tenderloin and ice-cream. A copy of the menu was spotted in a photo posted on social media by Education Minister Ong Ye Kung, who was present at the lunch.

Besides the menu, Ms Tan had to scrutinise the table's flower arrangements, portion sizes of the food, and even clocked the number of minutes that each course would take.

"If the portion sizes are too little, it may come off (like) we are not generous enough. If it's too big, there will be (wastage), so it's about striking a balance," she said.

"Essentially, all that is done is meant to facilitate the (diners') conversation, to allow PM Lee and president Trump to have a good conversation in an informal setting," she added.

For Ms Tan, who joined MFA only in 2015, the magnitude of the historic occasion sunk in when she saw the two leaders in the flesh.

"Seeing them in person… I thought — wow — I'm actually part of this historic moment. Even though it's short and even if our role was quite confined to the Istana, just the weight of the event and knowing that it's taking place in Singapore, it has been quite a privilege and an honour," Ms Tan said.