Taiwan said Sunday it would stop construction at a controversial nuclear power plant after tens of thousands of protesters blockaded a main street in the capital calling for the project to be scrapped.

Protesters broke through a police cordon to take control of a busy eight-lane intersection demanding an end to construction of the "Nuke Four" power station outside Taipei.

Later Sunday the ruling Kuomintang party yielded to pressure from the anti-nuclear demonstrators and promised to stop work at the plant.

"There will be no further construction of reactor one," Kuomintang spokesman Fan Chiang Tai-chi told reporters.

"Only safety checks will be done and after that it (reactor one) will be sealed for storage. Construction of reactor two will be terminated," he said.

"In the future, any of its commercial operation will be decided by a referendum."

Protest leaders said Sunday night that they were holding a meeting to discuss the announcement.

Chanting crowds gathered Sunday morning in the square outside the presidential palace where some protesters had already been staging an overnight sit-in.

Shouting "Stop construction of a fourth nuclear power plant!", demonstrators marched to nearby Chung-shiao West Road -- an eight-lane artery where the main railway station is located -- and swarmed through police lines to occupy the street, bringing traffic to a halt.

Around half an hour later, the outnumbered riot police, who had offered no resistance, retreated from the middle of the road to wild applause and cheers from the crowd, an AFP reporter on the scene said.

Buses and other vehicles were forced to detour around the intersection and traffic ground to a halt.

Police put protester numbers at around 28,500.

- Mounting public concern -

The demonstrators pledged to continue their sit-in until Tuesday, when parliament is due to meet to discuss the power plant.

"If Taipei citizens complain about the traffic tomorrow, they should blame President Ma Ying-jeou," an activist said through a loudspeaker as she stood on top of a van.

The power station has been one of the most contentious projects in Taiwan. Intense political wrangling has repeatedly delayed its construction, which began in 1999 and has already cost around Tw$300 billion ($10 billion).

Concerns about Taiwan's nuclear power stations have been mounting since 2011, when Japan's Fukushima nuclear plant was hit by a tsunami which knocked out power to its cooling systems and sent reactors into meltdown.

Like Japan, Taiwan is regularly hit by earthquakes. In September 1999 a 7.6-magnitude quake killed around 2,400 people in the island's deadliest natural disaster in recent history.

Taiwan's three existing nuclear power plants supply about 20 percent of the nation's electricity and the fourth plant is almost complete.

The main opposition Democratic Progressive Party opposes the facility on safety grounds, while the Kuomintang party says the island will run short of power unless it goes ahead.

Respected former opposition leader and devoted anti-nuclear campaigner, Lin Yi-hsiung, brought the issue into the spotlight once more on Tuesday when he started an indefinite hunger strike against the new power plant.

The 72-year-old activist said he had been forced into making the drastic move because the authorities had ignored majority public opinion against the power station.

Ma on Friday promised to let the public decide the fate of the facility in a referendum, but gave no timetable for the vote.