Today (1 May) the Expo 2015 (Universal Exposition) has opened in Milan and will run until 31 October.

Gates opened two hours before the official start of the fair, to let in hundreds of people that were already queuing outside the site early in the morning.

Italian Prime Minister Matteo Renzi is to cut the ribbon at midday local time and is then expected to visit the Nepalese pavilion first, to pay tribute to the more than 5,000 victims of the earthquake that hit the Himalayan country last week.

Pope Francis is also to make a video address at the opening ceremony, underscoring the importance of the exhibition theme, "Feeding the planet and Energy for Life", to the Vatican, which has its own pavilion centred on a subject dear the pontiff: the fight against what he says is modern society's "culture of waste".

The aim of the six-month-long exposition is to "increase visitors' awareness of and seek their participation in the drive for: the right to food that is healthy, safe and sufficient; the environmental, social and economic sustainability of the food chain; and the preservation of taste and of food culture".

Expo Milan 2015
The Lombardia Region building advertising Expo 2015 in Milan where the World Exposition Milano 2015 will run from May to October OLIVIER MORIN/AFP/Getty Images

Some 145 countries will show their commitment to creating sustainable ways of producing and delivering food across the globe while guaranteeing the safeguard of the planet.

It is estimated that around 150,000 people will visit the venue every day, with a total of 20 million visitors over the six-month period. Organisers said they expected 200,000 people for the opening weekend only.

Renzi said 10 million tickets have already been sold days before the inauguration of the event, fuelling hopes the it will work as a driving force to pull Milan and the rest of the country out of its economic quagmire.

Although the exposition is welcomed by many, it has also been object of severe criticism by people from the so-called "No Expo" movement. One day before the opening, hundreds of students marched through the streets of Milan, as they believe the event will not benefit Italy but only corporations collaborating with it.

They also said thousands of people are volunteering at the Expo venues and claimed they are being exploited as they are working for free. IBTimes UK contacted the Expo 2015 for a comment but has not received any response at the time of publishing.

The building of the exhibition site was marred by a corruption investigation that resulted in construction delays, with some workers finishing off details as people poured into the exhibition, which was however largely completed.

Celebrations started on the eve of the opening, with several artists, including Italian singer Andrea Bocelli and Chinese Pianist Lang Lang preforming at a concert in Milan's Duomo square.

Find out more about Expo 2015.