Italy's nationalist Lega party is set to win the majority of the country's seats at the European Parliament, while its coalition partner in Rome has seen a slump in support.

Initial results — with over half the ballots counted — suggested that Lega would take around 34% of the vote against just 17% for the left-leaning Five Star Movement (M5S) — almost and exact inversion of the 2018 national election result. Lega took just 6.2% in the last EU ballot in 2014.

"Thank you Italy. We will use your trust well. The first party in Italy will change Europe," Lega's leader and Deputy Prime Minister Matteo Salvini said in a video posted on Facebook.

Political analysts have described the European election as a test of Italy's anti-establishment government that has been in power for about a year. Both parties are still the two biggest in Italy, but there has been a clear shift in public opinion between them.

In last year's general election, M5S gathered the most votes but over time it has lost support, while its coalition partner has gathered momentum. Given the growing popularity of Salvini, analysts have questioned whether he will trigger a snap election and potentially lead the next Italian government. Tensions between both parties have intensified over the last few months.