Turkey is home to more than 3.6 million Syrian refugees and recently called for a "safe zone" in the war-torn country's northeast, to which refugees could return.
If the safe zone does not happen, "we will be forced to open the doors. You either give support, or if you won't, sorry, but we can only put up with so much," Erdogan said.
"Are we going to shoulder this burden alone?" he asked during the televised speech in Ankara.
Erdogan claimed Turkey had spent $40 billion on refugees and criticised the West, especially the European Union, for failing to live up to its promises.
Under a 2016 agreement, the EU promised Ankara six billion euros ($6.6 billion) in exchange for stronger controls on refugees leaving its territory for Europe, but Erdogan said only three billion euros had so far arrived.
"We may be forced to do this (open the gates) to get this (international support)," he said.
EU Commission spokeswoman Natasha Bertaud denied the claim later on Thursday, telling reporters in Brussels that the EU had provided 5.6 billion euros to Turkey under the agreement, with "the remaining balance due to be allocated shortly".
Turkey fears a fresh influx of refugees as the Syrian government advances into the last rebel stronghold of Idlib.
It also hosts hundreds of thousands of Iraqis and Afghans fleeing conflict in their countries.
In a bid to pressure the United States, which is to jointly patrol the safe zone, Erdogan said Turkey was "determined to set it up by the last week of September."
He added that 350,000 Syrians had already returned to parts of the country brought under Turkish control during offensives in 2016 and 2018.
"Our goal is to settle at least one million of our Syrian brothers and sisters in a safe zone along the border 450-kilometres long," he said.
