The Australian Broadcasting Corp. said the Timorese leader was rushed to hospital in Darwin for surgery.
Ramos Horta was shot in the arm and stomach after rebel leader Alfredo Reinado led a predawn raid on the home of the president in Dili, the Timor-Leste capital. Reinado was killed dead by Ramos Horta's guards.
Earlier, Australian Prime Minister Kevin Rudd told a news conference in Canberra that the government was sending an extra 120 troops and 70 police officers to boost the Australian peacekeeping force in Timor.
Rudd said Ramos Horta's condition was "very serious but stable."
"For there to be a coordinated attempt to assassinate the democratically elected leadership of a close neighbor and friend of Australia is a deep and disturbing development," Rudd said.
Rudd said he had spoken to Timorese Prime Minister Xanana Gusmao, whose car was also shot at Monday but who escaped unhurt.
He said he intended to take up an invitation from Gusmao to visit Timor-Leste this week.