The number of people arrested by police supervising the eviction a group of gas pipeline protesters from trees near Brecon, Powys, has risen to six.
The main A40 road has been closed during the evictions
The five men and one woman were being questioned on suspicion of obstructing a High Court enforcement officer.
More than 30 people have been protesting against a section of the pipeline, which will stretch from Pembrokeshire to Gloucestershire.
National Grid won a court order allowing it to evict the protesters.
Earlier, a company spokeswoman said the eviction was in "its early stages" and that she did not know how long it would last.
A High Court judge in Cardiff granted National Grid immediate possession of the occupied land. and issued an injunction forbidding trespass and damage to machinery on 14 June.
A large number of police and High Court officers have moved onto the temporary protest camp and the main A40 road has been closed to traffic while the eviction takes place.
The National Grid spokeswoman said it could not say whether any protesters had been removed yet.
She said: "The protesters are trespassing and the owners have asked them to leave.
"However, the protesters have failed to do so and the High Court officers supported by police are removing them this morning in accordance with the court order."
The protestors have set up camp in the trees
Dyfed-Powys Police said they were at the scene "performing an objective role in maintaining law and order whilst the High Court officers undertake their duties".
The protesters told the High Court judge their action was a non-violent peaceful expression of their rights.
When complete, the pipeline will run from Milford Haven to Gloucestershire and eventually supply up to 20% of the UK's gas needs.
The £840m project has faced a number of setbacks, including several protests against the first phase of the pipeline at Trebanos in the Swansea Valley.
In May, five protesters who prevented work on the Trebanos site in January pleaded guilty to aggravated trespass.