The former Greens MEP said, "I was riding directly past the station when I heard a very loud boom, an explosion. A large truck was passing at the time and at first I thought there had been an accident. The next thing I knew people were running from the station and there was smoke coming out of the entrance."
The former German MEP, who was visiting the European Parliament, added, "I was in the Parliament when 9/11 happened and there is a similar atmosphere today as there was that day, the only difference is that then people were talking to each other but now they walk around like zombies, only looking at their mobile devices.
"Normally, Tuesday in Parliament is like a busy Saturday market but, today, it is more like a Sunday morning."
Meanwhile, security in the European Parliament has been increased to "orange" - the highest possible alert.
It had already been at "yellow", the third level, since the Paris attacks but was changed after the double explosion at Zaventem airport.
All events and committee meetings have been cancelled for the day.
It is understood that visitors are not being allowed to enter the building, only accredited personnel such as MEPs and their staff.
Currently, only one door is open for people to enter and exit in the vast complex.
When I tried to enter the Parliament after the attack, I was met by a small army of security guards who, along with half a dozen Belgian soldiers, have erected what amounts to a ring of steel around the buildings.
For the first time since the Paris attacks soldiers patrolling the Parliament were wearing steel helmets.
A security guard said, "Not surprising after the events of today, the situation here is pretty tense at present."
However, contrary to some reports, people are being allowed to leave the Parliament if they wish.
An email was sent to all Parliament staff which announced, "The Belgian authorities have announced that the national alert level 4 passes on the entire territory.
"Therefore, the President (Martin Schulz) has decided to raise the level of the Institution alert in Brussels at orange with immediate effect."
It goes on, "A safety device is reinforced already in force and involves:
- Control of people and bags to the inputs (except for members);
- The closure of all entrances of the main buildings except for the entrance ASP Simone Veil;
- Systematic checks at the entrances of the peripheral buildings that will be strengthened by security personnel;
- The closure of the Parlamentarium;
- Systematic checks of vehicles entering parking lots."
The emailed message adds that staff "will be kept informed but you are asked to stay in buildings until further notice."
Meanwhile Brussels mainline train stations are set to re-open from 4pm according to the latest reports.