DUBLIN (Reuters) - It would be very important for Ireland that Britain retains its access to the European Union's single market in the event it votes to leave the union this week, Ireland's finance minister said on Tuesday.

Ireland's nearest and largest trading partner could lose its unfettered access to the EU's single market of over 500 million consumers if it decides to leave the 28-member bloc in Thursday's referendum.

While Norway is part of the single market via a trade deal it has with the EU, fellow non-EU member Switzerland only has access to bits of the single market and German Chancellor Angela Merkel has said Britain would lose full access if it left.

"I think it would be very important for Ireland that the single market with the EU would continue because they're our biggest customer," Noonan told national broadcaster RTE, referring to Britain.

"In any post-Brexit negotiations, we will be doing everything we can to assist the UK on the basis that they are our nearest neighbor and biggest customer."

Noonan, who earlier on Tuesday said a Brexit-related hit to the Irish economy would be "containable", added that he was optimistic that Britons would vote to stay in the EU.

(Reporting by Padraic Halpin; Editing by Catherine Evans)