* Agrees to buy WestLB Brazil unit for about Y30 bln-source
* Japanese banks buyers of overseas assets amid European retreat (Recasts with announcement, adds details)
TOKYO, June 20 (Reuters) - Mizuho Financial Group said on Wednesday it had agreed to buy a Brazilian unit of Germany's WestLB, the latest move by a Japanese bank to snap up assets amid the euro zone crisis.
Mizuho, Japan's second-largest lender by assets, did not disclose the terms of the deal, but a source with knowledge of the matter said it was paying about 30 billion yen ($380 million) for the 100 percent stake in the Brazilian bank.
Japanese banks, which have little exposure to Europe's troubled economies, are aggressively expanding lending overseas and buying up assets as European rivals retreat to weather the turmoil at home.
Banco WestLB do Brasil SA focuses on wholesale banking, with total assets of about $1.5 billion and hires 66 employees, Mizuho said in a statement. The Japanese bank has only a representative office in the South American country.
The acquisition is aimed at tapping the growing economies of South America, to counter sluggish demand for loans felt by Mizuho and its Japanese rivals in their home market.
Mizuho said it was expecting to lure Japanese and Asian clients who are expanding their businesses in Brazil and surrounding markets.
Japanese trade firms, including Mitsubishi Corp, are buying commodities assets in Latin America. Takeda Pharmaceutical, Japan's top drugmaker, said last month it would buy Brazil's Multilab for up to 540 million Brazilian reals ($265 million).
The deal is the latest by a Japanese bank to buy assets from a troubled western rival. Sumitomo Mitsui Financial Group , Japan's third-largest bank, earlier this month completed the $7.3 billion acquisition of RBS Aviation Capital from Royal Bank of Scotland.
WestLB, once Germany's third-largest landesbank, owned by the German state of North Rhine-Westphalia (NRW) and local savings banks, has been shrinking its business after receiving billions of euros of state aid during the global financial crisis. ($1 = 79.0300 Japanese yen) (Reporting by Taiga Uranaka; Editing by Richard Pullin and Jacqueline Wong)