Eight people were also wounded in the shooting at Suruc in the Sanliurfa region that broke out as MP Ibrahim Halil Yildiz visited small businesses in the town centre, the Anadolu and Dogan news agencies said.
He escaped unharmed, the reports said, but the identity of all the victims was not immediately clear.
There were conflicting reports about the circumstances of the killings, with pro-government media saying Yildiz and his supporters came under attack from opponents armed with knives and sticks.
The state-run Anadolu described it as an attack against the ruling Justice and Development Party (AKP) and added that among those killed was the brother of the MP.
It claimed that supporters of the pro-Kurdish Peoples' Democratic Party (HDP) were among those involved in the attack.
But unconfirmed reports on pro-Kurdish media blamed bodyguards of the MP for the attack, after he was met with hostility during the visit to the shopkeepers.
Suruc, a mainly Kurdish town, was the scene of a bombing on July 20, 2015, blamed on so-called Islamic State (IS) jihadists that killed 34 people and wounded about 100.
That bombing sparked huge tensions in Turkey at the time, with many Kurdish activists taking to the streets and accusing the government of not doing enough in the fight against IS.
Turkey is entering what is expected to be a tense final week of campaigning ahead of the polls.
Analysts are forecasting that the parliamentary and presidential elections will be tight, with Erdogan possibly to be pushed into a run-off and with his ruling party at risk of losing its overall majority.
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