British police have launched an investigation after a "Happy Brexit Day" sign was posted in a block of flats telling residents that "we do not tolerate" people speaking languages other than English.

The unsigned note was found in Winchester Tower in Norwich, eastern England, on Friday morning, hours before the UK officially left the European Union at 2300 GMT after 47 years of membership.

The poster reads: "As we finally have our great country back...we do not tolerate people speaking other languages than English in the flats."

"We are now our own country again and the the [sic] Queens [sic] English is the spoken tongue here.

"It's a simple choice obey the rule of the majority or leave," it went on.

According to the BBC, the posters were stuck on the fire doors of all 15 floors of the block of flats.

Norfolk Police confirmed to Euronews in a statement that "the matter is being dealt with as a racially aggravated public order incident".

"There is no place in society for hatred and intolerance. Nobody should have to face intimidation because of who they are and it is more important than ever that we stand together in the face of hostility," it added.

The Norwich city council had said on Saturday that the town "has a proud history of being a welcoming city, and we will not tolerate this behaviour."

"We take this very seriously and encourage residents to contact us or the police if they have any concerns.

According to data from Her Majesty’s Inspectorate of Constabulary and Fire & Rescue Services, a police watchdog, the total number of hate crime in England and Wales rose by 57% between 2014/2015 and 2016/2017.

The Brexit referendum was held in June 2016.

The watchdog had also warned the country's police forces in 2018 to prepare for a spike in hate crimes in 2019, as the country was initially scheduled to formally exit the EU in March 2019.