Despite enjoying strong ties with the Kurdistan Regional Government (KRG), Turkey fears today's vote could stoke separatist aspirations among its own Kurdish minority. Erdogan also hinted the Turkish military were ready to act if needed.
"Entrance-exit will be closed" at the Habur border crossing, Turkey's sole land border crossing with Iraq, Erdogan said in a speech in Istanbul.
He said there were currently crossings allowed to the Iraqi side only but travel would be closed in both directions this week.
Iraqi Kurdish oil is exported through Turkey and its southern Ceyhan port, a key economic lifeline for the region.
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Erdogan said "irrespective of the result, we see this (referendum) as null and void and say it is illegitimate".
Erdogan said Turkey was ready to take "all the steps" needed "on political, economic, trade and security fronts" and appeared not to rule out military action.
Last week the Turkish armed forces began a military drill in the region around the border town of Silopi including 100 military vehicles, which continued with reinforcements this weekend.
Erdogan warned the KRG of a cross-border operation by the Turkish army similar to that taken in northern Syria last year against the Islamic State group and Kurdish militants.
Dubbed Euphrates Shield, Ankara supported Syrian opposition fighters in northern Syria clear territory from IS and stop Syrian Kurdish militia from joining up their northern cantons. The operation -- begun in August -- was completed in March.
Turkey views the YPG and the PYD as "terror groups" linked to the outlawed Kurdistan Workers' Party (PKK), which has waged a separatist insurgency inside Turkey since 1984 and has its rear bases in northern Iraq.
Recalling the lighting offensive that kicked off Euphrates Shield, he added: "As I said, we can come unexpectedly in the night."
"We did this with Euphrates Shield. All the options are on the table right now," Erdogan said, adding: "In Iraq, when necessary, we will not shy away from taking these types of steps.