Tata Motors' factory to manufacture the world's cheapest car in Singur continued to remain under siege for the fourth day on Wednesday, as the opposition Trinamool Congress announced stepping up protests seeking return of farm land from the industrial house.

Hundreds of trucks remained stranded on the Durgapur Expressway, as demonstrators blocked movement of vehicles.

Trinamool Congress chief Mamata Banerjee, whose partymen have laid a siege to the plant obstructing work on the Rs one lakh car 'Nano', has called for a two-hour statewide road blockade on Friday after the West Bengal government rejected her demand for return of 400 acres land to farmers.

At an industry meet on Tuesday, Chief Minister Buddhadeb Bhattacharjee said he cannot afford to do that.

"If that land has to be returned, (then) Tata Motors project has to be dropped. I cannot allow this to happen," he had said, while also denouncing shutdowns as a means of protest.

"I will not support any bandh. We will not allow gherao-type agitation to take place in West Bengal," he had said.

Last week, Tata Group Chairman Ratan Tata had threatened to shut the Rs 1,500 crore project, citing continued protests and violence at the project site.

The work at project site is reportedly suffering as casual workers have not been able to report for duty.