Jones was answering journalists' questions before going into the House today at 2pm.
It is understood that Jones started to fell unwell during Question Time.
Reti, the MP for Whangarei and a doctor, was asked to take a look at Jones and recommended he be sent to hospital for tests.
Speaking to the Herald, NZ First Leader Winston Peters said Jones had been working extraordinary hard over long hours, day after day without breaks.
"It's a case of exhaustion I think, and we will find out."
He is waiting for more information.
NZ First MP Clayton Mitchell declined to comment, saying only: "I understand he's well and fine and just needing a bit of rest."
A spokeswoman for Wellington Free Ambulance confirmed that it had transported one person in moderate condition to Wellington hospital this afternoon.