Aug 13 (Reuters) - Foreign investors scaled up purchases in Japanese shares in the week ended Aug. 6 as optimism about strong corporate earnings outweighed concerns about surging cases of the Delta coronavirus variant.

Foreigners bought Japanese shares worth a net 398.7 billion yen($3.61 billion), their biggest net buying since the week to May 28, data from Japanese exchanges showed.

They purchased derivatives worth a net 327.67 billion yen and 71.03 billion yen in cash equity markets.

Cross-border investors also secured Japanese bonds worth a net 1.87 trillion yen, their second straight weekly net buying, finance ministry data showed.

Last week, Japanese shares marked their first weekly gain in three, thanks to domestic firms' upbeat quarterly results. Nippon Yusen, Misumi Group, auto-parts maker Denso reported strong earnings.

The Nikkei share average surged about 2%, while the Topix index added 1.5% last week, though concerns about a surge in COVID-19 cases that strained the local healthcare system lingered.

With about 95% of Japanese companies having reported their April to June quarter results, corporate earnings have jumped 135% from a year earlier and topped analyst estimates by about 28%, Refinitiv data showed.

Japanese investors purchased a net 615.7 billion yen in overseas equities, their biggest in over 14 months, but sold a net 965 billion yen in foreign bonds last week, finance ministry data showed. ($1 = 110.3500 yen)

(Reporting by Gaurav Dogra and Patturaja Murugaboopathy; Editing by Ramakrishnan M.)