Nia and Lana became Facebook friends. A day later, they had a baffling discovery.

Nia Hayes, from Indiana, always knew her dad had fathered another daughter before she was born.

The 35-year-old knew nothing about her older sister, besides the one baby picture that was included in the family photo album. When her father, Lonnie Hayes, passed away at 63 in 2012, she thought the secret had died with him.

All Lana Hayes, 42, knew about her father was that he and her mother had divorced when she was a baby.

She never saw him and only once tried to call him, when she was about 19. She looked up his number in the phone book, but hung up when a child answered the phone.

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Lana and Nia shared a mutual friend, Michael Hurst, who realised the two women looked eerily alike.

He persuaded them to add each other on Facebook. One day after they connected, Nia and Lana realised they were indeed sisters.

The pair also realised they had been living just over a kilometre apart for eight years without knowing.

"I feel like I'm looking at myself a little bit," Nia told King 5 News of meeting her long-lost sister.

"We're still getting used to it; we just keep looking at each other."

Lana said she had "no bad feelings" about being kept apart from her family for so long.

"I'm just excited," she said.

"My family has gotten a lot bigger. I've gone from one to seven siblings. It hasn't hit me yet. I'm thrilled, overwhelmed...I just feel so blessed."

The two believe their father is looking down on them and is happy they finally found each other.

"I think he's looking down and saying 'Finally, they're all together'," Nia said.