Televangelist and Crystal Cathedral megachurch founder Robert Schuller, known worldwide for his weekly "Hour of Power" broadcasts, died in Southern California on Thursday, his grandson said.

The 88-year-old Schuller had been diagnosed with esophageal cancer in 2013. His widely-viewed television broadcasts featured celebrity guests and drew tens of millions of viewers.

"My Grandfather Robert H. Schuller passed this morning into eternal life with Christ," Pastor Bobby Schuller said in a post on Twitter.

Supporters had said on Wednesday that the elder Schuller's condition was swiftly declining, and they called for prayers for him and his family.

"What a man! Thank you Dr Schuller ... So glad we lived in your time!" read a testimonial posted by one mourner on the Facebook page of Shepherd's Grove, which hosts Crystal Cathedral Ministries' services.