At least a dozen Turkish tanks have rolled across the Syrian border after heavy Turkish shelling of an area held by ISIS.
Military sources told Turkish media 70 targets in the Jarablus area had been destroyed by artillery and rocket strikes, and 12 by air strikes.
Turkish special forces entered Syria earlier as part of the offensive.
President Recep Tayyip Erdogan said the operation was aimed against both ISIS and the American backed YPG and PKK Kurdish fighters.
Turkey shelled Syrian Kurdish forces in the region this week, determined not to let them fill the vacuum if ISIS decides to leave the key city of Jarablus.
This is Turkey's first known ground incursion into Syria since a brief operation to relocate the tomb of Suleyman Shah, a revered Ottoman figure, in February of last year.
Erdogan's main concern is that the Kurds could create an autonomous area close to the border which might foster Kurdish separatism within Turkey itself, so they are determined to stop that, even if it means sending the Turkish army into Syria.
The Turkish plan is to cleanse the area from ISIS and to let Turkish backed Syrian rebels take contol of the city and the surrounding area.
The Turkish tanks were followed by pick-up trucks believed to be carrying Turkish-backed Syrian rebels from the Free Syrian Army.