TORONTO, May 12 (Reuters) - Manulife Financial Corp shares fell to their lowest level since January 2021 after the company's first-quarter core earnings declined due to lower sales and new business disruptions in Asia as COVID-19 infections rose in some parts of the region.

Both Manulife, and rival Sun Life, which also reported a drop in underlying profit driven by higher U.S. claims from the pandemic as well as lower sales in Hong Kong, said they expect the impacts of COVID-19 to linger.

Manulife missed analysts' estimates, while Sun Life beat expectations.

Manulife shares dropped 9.4% to C$22.06, their lowest intraday level since December 2020. Sun Life shares fell 2.4% to C$61.20. The broader Toronto stocks benchmark lost 0.8%.

The resurgence seen in the first quarter, most notably in Hong Kong, was "temporary in nature... but it's not necessarily true that we'll see an immediate bounce back in one quarter," Roy Gori, Chief Executive of Manulife, Canada's biggest life insurer, said on an analyst call.

Gori said the company still believes the "Asia opportunity is undeniable," and reiterated the company's goal of achieving half of core earnings from the region by 2025.

CIBC analysts said in a note that persistent growth challenges in Asia mean the company could miss analysts' expectations for the fiscal year.

Sun Life, Canada's second-biggest life insurer, is seeing "significant" improvement in U.S. death claims, Daniel Fishbein, president of its U.S. insurance business, said on its analyst call. But "we don't think that COVID is going away completely, and we do think there will be elevated mortality for a significant period of time."

The insurers also noted challenges from market volatility and the impact of inflation on expenses, but said the benefits from higher interest rates would help offset some of this. (Reporting By Nichola Saminather; Editing by Nick Macfie and Chris Reese)