The streets of Berlin were flooded with an estimated 150,000 protesters tonight, as furious activists campaigned against a controversial free trade deal between Europe and the United States.

Demonstrators hammered drums, blew whistles and brandished banners protesting the ‘anti-democratic’ deal, which would give corporations the right to sue governments in secret courts.

If the deal, the Trans-Atlantic Trade and Investment Partnership (TTIP), goes ahead, its supporters hope that it will deliver more than $100billion (£65billion) of economic gains on both sides of the Atlantic.

But critics fear the pact with the U.S. would hand too much power to big multinationals at the expense of consumers and workers.

Huge crowds: Demonstrators flooded the streets of Berlin today in protest against the proposed Trans-Pacific Trade and Investment Partnership, which would knock down trade regulations between the U.S. and EU

Protesters: Critics of the proposed free trade deal claim it would hand too much power to big multinationals at the expense of consumers and workers

They further claim that it would lower food safety, labour and environmental standards, risk the privatisation of Britain's National Health Service, and cause higher unemployment.

Of great concern for those speaking out against the deal is the fact that the majority of negotiations have taken place behind closed doors - giving rise to allegations of 'secrecy'.

The organisers for tonight’s event, who claim that the number of attendees was closer to 250,000, include environmental groups, charities and opposition parties.

‘This is the biggest protest that this country has seen for many, many years,’ Christoph Bautz, director of citizens’ movement Campact, told protesters in a speech.

TTIP is mainly about knocking down regulatory barriers to trade for big business, which include food safety laws, environmental legislation, banking regulations and the sovereign powers of individual nations.

The TTIP deal is a companion agreement to the Trans-Pacific Partnership (TPP) trade deal, which was given the go-ahead in a landmark trade agreement reached earlier this week, between the U.S., Japan, and 10 other countries circling the Pacific Ocean.

But in an unexpected move Democratic leadership hopeful Hillary Clinton spoke out against the deal, saying ‘as of today, I am not in favour of what I have learned about it’.

Activists: The organisers for tonight’s event, who claim that the number of attendees was closer to 250,000, include environmental groups, charities and opposition parties

Fear: Protesters are concerned that the deal would destroy strict European food safety and environmental standards, in favour of laxer U.S. laws

Corporate power: Protesters are particularly fearful that the agreement would allow multinationals to sue governments if their policies interfere with profits

She told PBS’s NewsHour: ‘I don’t have the text, we don’t yet have all the details, I don’t believe it’s going to meet the high bar I have set.’

It marks a dramatic turn-around for Ms Clinton, who was instrumental in the negotiation stages while serving as secretary of state.

Smaller protests were also held in other cities across Europe, including Amsterdam and London.

The London protest was organised by the organisation War on Want and its allies.

‘Across the continent, people are outraged at TTIP’s assault on our society, health and environmental protections, privisation of our public services and use of “corporate courts” so big businesses can sue European governments for policies affecting their profits,’ the organisation said.

More than three million people have signed the #NoTTIP movement’s petition against the deal, including some 500,000 in the UK.

Opposition against the TTIP deal has been escalating in Germany over the past 12 months, since a proposed draft was leaked last year.

Powerful movement: More than three million people have signed the #NoTTIP movement’s petition against the deal, including some 500,000 in the UK

Shock: Opposition against the TTIP deal has been escalating in Germany over the past 12 months, since a proposed draft was leaked last year

Growing tide: If an agreement is reached on the deal, it is thought it won't come into effect until 2016 at the earliest

Dietmar Bartsch, the deputy leader of the parliamentary group for the Left party, who was taking part in the rally, said he was concerned about the lack of transparency surrounding the talks.

‘We definitely need to know what is supposed to be being decided,’ he said.

‘What bothers me the most is that I don’t want all our consumer laws to be softened,’ said demonstrator Oliver Zloty.

‘And I don’t want to have a dictatorship run by any companies.’

Chancellor Angela Merkel’s government has been stunned by the strength of resistance against the trade deal, underscoring the challenge it faces in turning the tide in its favour.

Economy Minister Sigmar Gabriel issued warnings against ‘scaremongering’, in a full-page letter published in several German newspapers on Saturday.

Resistance: Chancellor Angela Merkel’s government has been stunned by the strength of resistance against the trade deal, underscoring the challenge it faces in turning the tide in its favour

Twin plans: The TTIP deal is a companion agreement to the Trans-Pacific Partnership (TPP) trade deal, which was given the go-ahead in a landmark trade agreement reached earlier this week, between the U.S., Japan, and 10 other countries circling the Pacific Ocean

Key aims: TTIP is primarily about knocking down regulatory barriers to trade for big business, which include food safety laws, environmental legislation, banking regulations and the sovereign powers of individual nations

Demonstrators hammered drums, blew whistles and brandished banners protesting the ‘anti-democratic’ deal, which would give corporations the right to sue governments in secret courts

‘We have the chance to set new and good standards for growing global trade,’ he wrote.

‘With ambitious standards for the environment and consumers, and with fair conditions for investment and workers. This must be our aim.’

Ulrich Grillo, head of the BDI Federation of German industries, said in a statement: ‘A fair and comprehensive free trade deal promotes growth and prosperity in Europe. We should actively participate in the rules for world trade of tomorrow.’

If an agreement is reached on the deal, it is thought it won't come into effect until 2016 at the earliest.