MILAN, Jan 8 (Reuters) - Italian mid-sized lender BPER Banca said on Monday it has hired banks to sell an 'Additional Tier 1' (AT1) bond, the riskiest type of bank debt, adding to a busy day for Italian corporate debt issues.

This will be BPER's first AT1 bond marketed to institutional investors, after in 2019 it privately placed a previous issue with leading shareholder Fondazione di Sardegna.

The $275 billion AT1 market bounced back late last year from a shock bondholder wipeout during the Credit Suisse rescue.

AT1 bonds count towards banks' 'Tier 1' capital because they are designed in such a way that they can absorb potential losses.

BPER's upcoming AT1 issue is rated 'B+' by Fitch Ratings.

Reuters reported in December that Italian issuers, after a slow 2023, were expected to seize the traditional start of the year momentum in bond markets, including by selling AT1 debt.

On Monday, Italian insurer Generali drew around 4 billion euros ($4.4 billion) in demand for a two-part bond that qualifies as 'green' under the insurer's framework for social, sustainable and green debt.

Mediobanca sold 750 million euros of a 'covered' bond backed by residential mortgages, after receiving more than 1.2 billion euros in orders.

Demand for a 1 billion euro 10-year bond by state-controlled oil and gas group Eni totalled around five times that amount.

"Italy's primary debt market activity is in full swing," said Marco Spano, managing director and co-head of debt capital markets and financing at Mediobanca - a joint-bookrunner on all four transactions.

Spano said new issues hitting the market ranged from the most senior to the most junior type of corporate debt.

"There is demand for every category ... and we believe there could be more to come as far as Italy is concerned, after a very busy first week of January in the rest of Europe," he said.

Also the Rome-based Treasury on Monday said it had hired banks to manage the sale of a new seven-year BTP bond, a top-up of a 30-year BTP issue.

($1 = 0.9143 euros) (Reporting by Valentina Za and Sara Rossi; Editing by Louise Heavens and Susan Fenton)