All electioneering had to stop at 6 p.m., the Bangkok Post reported.
Prime Minister Yingluck Shinawatra, leader of the Pheu Thai Party, joined her candidate, Police Gen. Pongsapat Pongcharoen, in a car and truck caravan through the capital. Several cabinet ministers participated.
Sukhumbhand Paribatra, the Democrat candidate, was joined by former Prime Minister Abhisit Vejjajiva. A caravan of pickup trucks advertised Sukhumbhand's candidacy.
Late polls showed Pongsapat leading his rival, although both Pheu Thai and the Democrats said they believe the race is going to be a close one.