HELSINKI (AFP) - European Council President Donald Tusk said Thursday it was hard to be upbeat about the outcome of Britain's vote on whether to stay in the EU, but warned it made no sense for the country to quit.

"I know it's very difficult for us to be optimistic today, we know the latest polls," Tusk said on a visit to Helsinki a week before the referendum.

But he added: "Leaving now does not make any sense."

A new opinion poll published in Britain on Thursday by the Ipsos Mori group showed 53 percent in favour of a Brexit compared to 47 percent who want to stay in the EU.

It was a marked change from last month when the "Remain" camp was leading by 57 percent to 43 percent, excluding undecideds.

Tusk had warned on Monday that it Britain votes to leave the 28-member bloc on June 23, it would spell the "destruction" of Western political civilisation.