Christians have been offering their prayers and condolences on Twitter for TobyMac's family after his son's tragic death on Wednesday at the age of 21.

Harvest pastor Greg Laurie was among those asking Christians to pray after news of Truett Foster McKeehan's death emergedf. 

"Let's all be praying for@tobymac and his family as they mourn the passing of Toby and Amanda's son, Truett. May 'The God of all comfort' be with them," he wrote. 

The Billy Graham Evangelistic Association said: "Our prayers are with@TobyMac, a longtime friend of the ministry, as he grieves the loss of his oldest son.

"We pray that God's Word is a comfort to his family during this difficult time. 'The Lord is near to the brokenhearted and saves the crushed in spirit.' —Psalm 34:18." 

Gary Levox, lead singer of country group Rascal Flatts, said he was "heartbroken" for the family. 

"God draws himself closer to the broken-hearted. Everyone please cast a prayer over the family!" he told his fans. 

TobyMac was touring in Canada when he received the news about his son.  The remaining concerts were cancelled as he flew back to his home in Tennessee to be by his family's side. 

Fans of the longtime Christian rapper were familiar with his son Truett because of his frequent appearances on his dad's albums from a very young age. 

Truett appeared to be following in his father's footsteps as an aspiring rapper, going by the name of Trudog.

The Tennessean reports that the the Nashville Fire Department responded to reports of a person in cardiac arrest at a residence in the Radnor neighbourhood on Wednesday morning.

A representative for TobyMac, whose real name is Toby McKeehan, confirmed that Truett had passed away and asked for privacy at this time. 

"Cause of death has not been determined," they said.

"Toby was traveling back from Canada and did not get home to be with his family until after midnight last night so there is no statement.

"We just ask that everyone please be respectful of their privacy during this time and allow them to grieve their loss."

READ MORE: TobyMac releases statement on son's death: 'Truett always had a soft spot for God.'

READ MORE: Christian rapper TobyMac's son Truett Foster dies age 21