The business district and the presence of families,tourists and expatriates there, would make it difficult for security forces to move against the protesters.
"We believe the government will try to disperse us again in the next couple of days," Nattawut said.
"We're organising our movement to fight. We hope it will be the final round between us and this government."
Al Jazeera's Tony Birtley, reporting from Bangkok, said: "Before this [the protesters] had been dispersed in three locations in the city and two of them were quite vulnerable in case the army decided to have a crackdown.
"They are not at the moment, the army is still in the barracks, but if they were to those areas could be taken quite quickly.
"The commerical centre is much more difficult, there are much more compact streets, more places to hide and more places where barricades could hold up the military."
The rally in the commercial district has already blocked roads and caused shops to close their stores.
"They are holding the economy as their hostage," Boonyakiat Karavekphan, a political scientist at Ramkhamhaeng University, said.
The death toll from the violence in Bangkok's historic quarter, where the protesters had been based for more than a month, rose to 23 people on Wednesday, following the deaths of a soldier and a protester.
Blood can still be seen on the streets in the area and makeshift Buddhist shrines have been set up near wrecked army personnel carriers daubed with graffiti, such as "tyrant Abhisit".
The government has blamed "terrorists" for the violence and ordered police to hunt for those responsible.
"We believe there were terrorists who were ambushing in the area," Sansern Kaewkumnerd, an army spokesman, said.
The red shirts, many of whom supported the ousted prime minister Thaksin Shinawatra, are calling for Abhisit and his government to step down and call early elections.
Abhisit, who most political analysts had predicted would ride out the storm, has seen his position undermined by an investigation into the funding of his Democrat Party and comments from the country's army chief that new elections were the only
way out of the crisis.