Mr Suthep was speaking to huge crowds occupying the road between the Ratchaprasong and Pratunam intersections shortly before 4pm.
He described people power at the Sunday rallies as "massive" and said the number of protesters was far more than those at the rallies on Dec 9. However, he believed the government would tell other countries and foreign media that only 150,000 protesters showed up.
“The phenomenon today clearly confirms Thailand will survive and the Thasin-regime will be definitely eradicated.
“The people will keep on fighting until the Thaksin-regime is extinct and [caretaker premier] Yingluck resigns,” Mr Suthep said.
The protesters shouted “Get out, get out” intermittently during his speech.
He accused the red-shirt United Front for Democracy against Dictatorship (UDD) of holding a mass rally at the Ratchaprasong intersection in 2010 for the sake of ousted former premier Thaksin Shinawatra.
“They fought for one man which is their father in Dubai. The same place here, but we have millions of people but can remain peaceful. We kill no one and don’t torch the city.”
“Today we shut down Bangkok for half a day. If [Yingluck] does not resign, next time it will be a full day and if she still does not resign, it may be a whole month shutdown.”
After his appearance at the Ratchaprasong protest venue, Mr Suthep went to another rally site at nearby Siam Centre.