Security was extremely tight in Singapore on Tuesday for the historic summit between the leaders of the United States and North Korea, with whole roads blocked and barricaded in the vicinity of the venue and their hotels, and thousands of security personnel patrolling both on land and at sea.

Prime Minister Lee Hsien Loong said earlier this week that Singapore has spent $S20 million to host and organize the summit between U.S. President Donald Trump and North Korean leader Kim Jong Un on Tuesday, of which half is for one of the largest ever security operations in the wealthy city-state.

"We will do what is necessary to make this a safe meeting," Lee told local reporters.

Home Affairs Minister K. Shanmugam said 5,000 security officers had been deployed on the ground, with national servicemen also roped in to help.

"We are very happy to play a part in facilitating this meeting with Singapore being the venue. It says much that both (North Korea) and the U.S. have agreed on Singapore," Shanmugam said.

"Both take security very seriously, their leaders are high-profile targets, they believe that Singapore can provide a safe, secure venue and they have confidence in our neutrality, so it's a major show of confidence in Singapore."

About a week before the summit, the government designated the areas around the St. Regis and Shangri-La hotels, where the two leaders were staying, near the bustling Orchard Road shopping enclave, as special security zones, which would allow the police to conduct tighter checks on cars and people or even deny access altogether.

At the St. Regis hotel where Kim was staying, a huge white tent has been erected nearby for use by security officers, while a whole stretch of road beside the hotel has been heavily barricaded to keep vehicles out. Dozens of police motorcycles, along with ambulances and fire engines and other rescue vehicles, were parked nearby.

The security was stepped up even for airplanes arriving at Changi airport, a major regional air hub, with planes told to slow down their speed. More patrols are being conducted in waters surrounding the resort island of Sentosa where the summit venue, the Capella Singapore hotel, is located.

A Singapore air force drone is providing aerial surveillance over the island during the summit, while the Singapore navy has stepped up maritime patrols in the waters around Sentosa, according to the Defense Ministry.

With more than 2,000 foreign journalists having registered to come to Singapore for news coverage of the event, the F1 Pit Building in mainland Singapore is being used as the media center.

Police arrested two South Korean media personnel for criminal trespass at the house of the North Korean ambassador on June 7. The two men, aged 42 and 45, were deported to South Korea.

Immigration authorities have also turned away at least four people in the days before the summit, including a Southeast Asian man who was behaving nervously and was suspected of having visited internet sites related to suicide bombings, and an Australian man who was denied entry on account of his previous alleged terror-related activities.

Even Howard X, a comedian who entertains by impersonating Kim, was detained by police for about two hours when he arrived at Changi Airport on Friday. "I think the immigration officers wanted to intimidate me. They said not to go to Sentosa," he said.

(Howard X)

John Shaw, a British tourist on holiday with his wife soon after retiring as a police officer, said he felt very safe, and was impressed with the way the security was organized for the summit.

"This is very, very well organized," he said. "It's possibly one of the biggest events in world history, so it's justified."

Helen Chin, a Singaporean woman in her 60s who works as a store clerk, said she found the security arrangements troublesome as she cannot take a bus to her workplace because the stretch of road has been closed off to vehicles, while she doubted that most Singaporeans are excited about the summit.

While Singapore is regarded as one of the safest places in Asia, it is said to be targeted by terrorists due to its close relations with the United States and Israel.

In 2016, Indonesian militants allegedly plotted to launch a rocket attack from Indonesia's Batam island, which is a 45-minute ferry ride away, toward Singapore's Marina Bay financial district.