Hundreds of factories are shut in the Indonesian capital Jakarta as thousands of workers began gathering to protest against unsuitable conditions.

It is estimated that some two million factory workers will go on strike nationwide on Wednesday.

In Jakarta, about 800 factories were closed as workers gathered to protest, Al Jazeera's Stepp Vaessen reported from the scene of a strike.

"I'm at the biggest industrial zone outside of Jakarta where 800 factories are basically closed down right now because all the workers are standing outside on the streets with banners and motorbikes going around," she said on Wednesday.

"They are waiting for other workers from other factories in the area to gather here and have a huge protest."

Vaessen said protests were under way outside of factories all over the country.

"An estimated two million workers are on strike today.

"They are protesting against their working conditions and over the work contacts that they have. They say they don't have any job security and no stability," she said.

The Jakarta Globe newspaper reported on its website that the unions were expecting some 2.8 million people to go on strike in 21 districts and municipalities and 80 industrial zones across the country.

The newspaper said the largest demonstration would involve some 500,000 people.

It also said the workers were protesting against the practice of outsourcing manpower.

The strikes could threaten Indonesia's economy which has been held up as a success story in recent years.