Protesters prevented environment minister Barbara Hendricks leaving for climate talks in Paris by chaining themselves to the railway tracks in Frankfurt. She was traveling with 30 of her staff.
As Hendrick's train pulled into Frankfurt station on Saturday en route to the French capital, protesters chained themselves to the railway tracks, police said.
Others descended by ropes onto the train, which stopped in Europe's financial capital en route from Berlin where Germany's environment minister and her 30-strong entourage had boarded.
Hendricks and her team were traveling to Paris for the global climate change conference which gets underway on Monday.
German journalist Harriett Wolf tweeted that as the demonstrators had refused to come down, officers had no choice but to climb onto the train's roof.
Officials said it took about two hours to unchain the protesters from the tracks. Six people were arrested.
A spokesman for the minister declined to comment on the incident.
The meeting of world leaders and environment groups is meant to steer the global economy away from reliance on fossil fuels.
The goal is to stop the global temperature from rising more than 2 degrees Centigrade over pre-industrial times, in order to avoid catastrophic loss of human life from rising sea levels and severe weather patterns.
Hendricks is hopeful
Earlier on Saturday, Hendricks said she has high hopes that a new world climate agreement will be finalized at the summit, which lasts until December 11.
Hendricks said that a deciding factor for an agreement is that both so-called developing countries and industrial nations take part in financing climate measures and projects.
Several scientific studies project that pledges made so far will - at best - hold the world to temperature rises of anywhere from 2.7 to 3 or even 3.5 degrees above pre-industrial times by 2100, well above an agreed 2-degree UN limit.
More than 40,000 people are converging on the French capital for the summit, including 10,000 delegates from 195 countries.
Security has been stepped up in the wake of the Paris Attacks on November 13. About 2,800 police and soldiers will secure the conference site, and 6,300 others will be deployed throughout the city.
Also on Saturday, tens of thousands of protesters gathered in cities from Auckland to London calling on world leaders to avoid a climate catastrophe.
Further rallies are planned for Sunday in Seoul, Rio de Janeiro, New York, Kiev and Mexico City.
In Paris, French authorities canceled two demonstrations following the mass killings of 130 people earlier this month.
But activists still plan to create a two-kilometer (1.2-mile) human chain along the original march route on Sunday.
They will break the chain as they pass the Bataclan concert hall, where the worst violence claimed 90 lives, as a mark of respect to the victims.
Protesters also plan to leave scores of shoes on Place de la Republique square to symbolize the thousands left frustrated in their plans to march.
mm/rc (AFP, dpa)