Shares of Massey Energy fell nearly 10 percent the day after an explosion at one of its coal mines in West Virginia killed at least 25 workers.

In early trading on the New York Stock Exchange on Tuesday, the company's shares were down $5.33, or 9.8 percent, at $49.36.

The cost of protecting Massey's debt against default also rose after the blast at the Upper Big Branch mine. Massey's five-year credit default swaps rose to 385 basis points from 365 basis points on Monday, according to data from Phoenix Partners Group.

However, analysts at Jefferies & Co maintained their buy rating on Massey shares.

We believe Massey Energy is a well-capitalized Eastern coal producer and ranks as the largest, most diversified, and lowest-cost coal producer in Central Appalachia, they wrote in a research note.

With a favorable product mix, well-capitalized infrastructure, and solid margin generation in a very difficult market, they wrote, we believe the shares appear under-priced.

(Reporting by Steve James; Editing by Lisa Von Ahn)