Cape May, N.J. — An off-duty Philadelphia firefighter has died at a Cape May triathlon, fire officials confirm to CBS Philadelphia. The firefighter was competing Sunday morning in the Escape the Cape Triathlon.

It is unclear how the off-duty firefighter died at this time.

The triathlon consists of a 1-mile swim, a 23-mile bike ride and a 5-mile run. Swimmers began jumping off the Cape May-Lewes Ferry around 8:30 a.m. Sunday for the first leg.

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Another Philadelphia firefighter also died Sunday morning from long-term medical issues.

Philadelphia Fire Commissioner Adam Thiel announced the news in a tweet.

We @PhillyFireDept mourn the untimely loss of 2 active (off-duty) PFD members today; please keep their families, friends, & colleagues in your thoughts during this difficult time. (**Details may be released in the future, according to the families’ wishes.**) — Adam K. Thiel (@ThielAdam) June 2, 2019

The identities of the firefighters have not been released at this time.