Thousands of protesters staged a sit-in near the presidential palace in Taiwan's capital on Saturday to oppose a controversial nuclear power plant and show support for a high-profile activist on hunger strike.

The protesters braved pouring rain in Taipei to wave banners and placards reading "No nukes, no fear" and "Abolish nuclear power," amid tight security.

Police sealed off some streets in the area with barbed-wire barricades as organisers vowed to stage more protests if their demands were not met.

The plant outside Taipei 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).

Lin Yi-hsiung, a respected 72-year-old former opposition leader who has devoted himself to the anti-nuclear cause in the past two decades, began an indefinite hunger strike on Tuesday to urge the government scrap the nearly completed facility.

Lin has said that he was forced into taking the drastic move because the authorities ignored majority public opinion against the power station.

"The matter is urgent as Mr. Lin has been on hunger strike for five days," said protest organiser Liu Hui-min.

"We demand the government to stop building the plant immediately or we will continue the sit-in indefinitely."

Taiwan's President Ma Ying-jeou on Friday promised to let the public decide the fate of the facility in a referendum, but gave no timetable for the vote.

Concerns about Taiwan's nuclear facilities have been mounting since 2011, when the Fukushima nuclear plant in Japan 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 deadliest natural disaster in recent history.

"The government keeps telling us nuclear energy is safe because developed Western countries are using it but they are not prone to earthquakes like Taiwan. The government should not risk our lives," said school teacher Tsai Ya-ru.

The main opposition Democratic Progressive Party opposes the facility on safety grounds, while the ruling Kuomintang party says the island will run short of power unless it goes ahead. Taiwan's three existing nuclear power plants supply about 20 percent of the nation's electricity.

Some protesters urged the government to put the issue to a vote as soon as possible.

"I think many people don't trust the government now so it's better to let the public make the decision and we will obey majority opinion," said pharmacist Lee Chun-yi.

Organisers expected a turnout of over 70,000 people for the round-the-clock sit-in, which will be followed by a march on Sunday. An initial police estimate of the crowd size was 8,500.