More than 33 years ago, the world’s worst nuclear disaster took place in a Ukrainian town near the Belarus border.

The Chernobyl nuclear disaster happened overnight on 25-26 April 1986 in the now-abandoned town of Pripyat, when an explosion sent radioactive material into the air.

As new Sky Atlantic/HBO drama Chernobyl premieres on 7 May, here’s everything you need to know about visiting the former nuclear site.

What is the Chernobyl disaster and what happened?

The disaster occurred during a routine late-night safety test in the number four nuclear reactor of the Chernobyl Nuclear Power Plant, in the town of Pripyat, which is 104k from the Ukrainian capital Kiev.

The plant crew intentionally switched off the safety systems to test the turbine.

Illegal tour of Chernobyl visits forgotten sites Show all 25 1 /25 Illegal tour of Chernobyl visits forgotten sites Illegal tour of Chernobyl visits forgotten sites Evening in the ghost town of Pripyat John Levin Illegal tour of Chernobyl visits forgotten sites A gas mask hangs in a building inside the Chernobyl Exclusion Zone Ryan Longstaff/SWNS Illegal tour of Chernobyl visits forgotten sites Remains of Soviet propaganda in one of the barracks of the abandoned anti-aircraft base Volkhov near the Chernobyl NPP John Levin Illegal tour of Chernobyl visits forgotten sites The shell of a television stands inside a building in the Chernobyl exclusion zone Ryan Longstaff/SWNS Illegal tour of Chernobyl visits forgotten sites A children's play area inside the Chernobyl exclusion zone Ryan Longstaff/SWNS Illegal tour of Chernobyl visits forgotten sites A Soviet-era classroom in the Chernobyl exclusion zone Ryan Longstaff/SWNS Illegal tour of Chernobyl visits forgotten sites Tourists inside the Chernobyl exclusion zone Ryan Longstaff/SWNS Illegal tour of Chernobyl visits forgotten sites Duga was a Soviet over-the-horizon (OTH) radar system used as part of the Soviet missile defense early-warning radar network John Levin Illegal tour of Chernobyl visits forgotten sites In the Pripyat abandoned apartments you can still see the abandoned belongings of evacuated residents of the city John Levin Illegal tour of Chernobyl visits forgotten sites "Ambulance car model RAF-2203 Latvija (nickname Rafik) on the background of the Medical Sanitary Unit 126 in Pripyat. It was a minibus designed and developed by Rīgas Autobusu Fabrika from 1976–1997. They were widely used throughout the USSR as medical cars. Model RAF-2203 also were used in Pripyat" John Levin Illegal tour of Chernobyl visits forgotten sites Remains of Soviet propaganda in one of the barracks of the abandoned anti-aircraft base Volkhov near the Chernobyl NPP Ryan Longstaff/SWNS Illegal tour of Chernobyl visits forgotten sites An empty swimming pool inside the Chernobyl exclusion zone Ryan Longstaff/SWNS Illegal tour of Chernobyl visits forgotten sites "Illegal Chernobyl explorers cross the Uzh river in the Chernobyl Exclusion Zone. This is the time when you can safely walk around the abandoned without fear of being caught by the police" John Levin Illegal tour of Chernobyl visits forgotten sites "A couple of years ago the Ukrainian army began to conduct military exercises in the city of Pripyat. Traces of bullets on the walls and glass of the city are not such a rare phenomenon in Pripyat today" John Levin Illegal tour of Chernobyl visits forgotten sites Interior of a flat in the Chernobyl exclusion zone Ryan Longstaff/SWNS Illegal tour of Chernobyl visits forgotten sites "Chernobyl explorer on the top of huge Soviet radar “Russian woodpecker” or Duga radar. As a rule, we climb up Duga radar at dawn. From a height of 150 metres you have an incredible view of the expanses of the Chernobyl zone" John Levin Illegal tour of Chernobyl visits forgotten sites Interior of a building in the Chernobyl exclusion zone Ryan Longstaff/SWNS Illegal tour of Chernobyl visits forgotten sites "The perimeter of the Chernobyl exclusion zone is protected by barbed wire. But this does not stop the fans of dark tourism" John Levin Illegal tour of Chernobyl visits forgotten sites The Ferris wheel in the amusement park of the ghost city of Pripyat is the hallmark of the city. This ferris wheel was supposed to be launched on May 1, 1986, but the Chernobyl accident destroyed these plans forever John Levin Illegal tour of Chernobyl visits forgotten sites "Pripyat is the main goal of many illegal Chernobyl explorers. To get to the city you need to walk about 40 km on foot. On the way to the ghost town, explorers spend the night in the abandoned villages of the Chernobyl zone" John Levin Illegal tour of Chernobyl visits forgotten sites The Pripyat Ferris Wheel John Levin Illegal tour of Chernobyl visits forgotten sites Interior of a flat in the Chernobyl exclusion zone Ryan Longstaff/SWNS Illegal tour of Chernobyl visits forgotten sites Interior of a building in the Chernobyl exclusion zone Ryan Longstaff/SWNS Illegal tour of Chernobyl visits forgotten sites From inside a kindergarten in the Chernobyl exclusion zone Ryan Longstaff/SWNS Illegal tour of Chernobyl visits forgotten sites Another view of the Pripyat Ferris Wheel Ryan Longstaff/SWNS

However, the reactor overheated and generated a powerful explosion that sent plumes of radioactive material two kilometres into the Earth’s atmosphere. It’s estimated that 400 times more radioactive material was sent into the air than when the atomic bomb dropped on Hiroshima, Japan.

Following the explosion, 134 servicemen were hospitalised with acute radiation sickness, of which 28 firemen and employees died in the weeks and months after the explosion.

An 18-mile radius, known as the exclusion zone, was set up around the reactor; and more than 100,000 people were evacuated from the area.

Is Chernobyl open to tourists?

Yes. The site has been open to the public since 2011, when authorities deemed it safe to visit.

Is it safe to visit?

Yes, provided you visit with a specialist tour guide.

“Several thousand people visit every year,” says Justin Francis, CEO of Responsible Travel. “The amount of radiation you’re exposed to is similar to on a long haul flight.

“The main danger is not radiation, but unsafe structures which have been deserted for 30 years, and lots of metal has been stripped away. So go around in groups, and obey the guide’s instructions.”

Peter Wybrow, Ukraine expert at Regent Holidays, which organises trips to Ukraine and Chernobyl, says guides will always carry a Geiger counter with them to measure radiation.

However, it is dangerous to stay near the site for longer periods.

Should tourists visit Chernobyl?

It’s a fascinating experience on many levels and well worth a visit, says Francis.

“It’s bleak but also illuminating, poignant, fascinating to learn the real stories. It’s a photographer’s dream.

“You can also meet the settlers who returned to hear their stories and help them out by buying their moonshine. Don’t see it as disaster tourism but as a way of understanding the risks of nuclear.”

If I want to visit, how can I do it?

Chernobyl is around 100k north of the Ukrainian capital Kiev, or a two-hour drive. It’s an easy day trip for tourists already in Kiev.

“Most tours are day trips but you can stay overnight in a small hotel in Chernobyl town too, which is perfectly safe and best way to really experience it rather than just a few hours on a day trip,” says Francis.

“Kiev shouldn’t be missed and it’s a good idea to combine with a visit to the Kiev Chernobyl Museum giving you the background, especially some interesting films shot during the time of the evacuation.”

What can visitors expect when they visit?

Because the exclusion zone has meant almost no human interference for more than 30 years, wildlife surrounding Chernobyl has thrived: visitors can spot species such as tame foxes and giant catfish, as well as wild horses, bison, bears and wolves – although these are rarely seen.

Francis adds: “There are also many interesting buildings around, although lots of them have been damaged by looters or disrespectful tourists.

“It’s a good idea to climb to top of a residential building, about 15 storeys high, to take in the views. Also the fairground, the Ferris wheel is one of the iconic Chernobyl images. It was scheduled to open a few days after the explosion so the wheel and the dodgems never had paying riders.”

What should tourists be aware of?

Some places are still off-limits to tourists because of radiation fears, such as the basement of the hospital where the first responders’ equipment and clothing was dumped, says Wybrow.

Although on a two-day tour to Chernobyl, visitors will be exposed to a lower level of radiation than on a long-haul flight, there are safety checks in place.

Wybrow adds: “When you go through the outer and inner exclusion zone you are subject to radiation checks to ensure no one is above a safe level. There is also a curfew in Chernobyl if you overnight there.”