A US Senate panel has voted to give President Barack Obama authority to "fast-track" a massive Pacific trade accord, adding a provision opposed by the White House that addresses currency manipulation.

In a marathon debate, the Senate Finance Committee considered dozens of amendments to the so-called trade promotion authority (TPA) legislation, a bipartisan measure that supporters say is crucial to getting the 12-member Trans-Pacific Partnership - deemed the largest free-trade agreement ever - across the finish line.

The panel voted 20-6 in support of the TPA bill, with five Democrats bucking their president and voting in opposition along with one Republican.

The debate came as US officials negotiate the ambitious trade pact with Australia, Brunei, Canada, Chile, Japan, Malaysia, Mexico, New Zealand, Peru, Singapore and Vietnam.

If the fast-track measure passes the full Senate and House of Representatives, it creates a simplified mechanism for congress to approve or reject any agreement negotiated by Obama, while preventing lawmakers from making changes.

The measure may have a tough road in the House.

"This bill has a long way to go" before it passes both chambers, House Speaker John Boehner said.

Senate Finance chairman Orrin Hatch pleaded with colleagues not to block the legislation.

Without it, he said, "our trading partners will not put their best offers on the table because they will have no guarantees that the agreement they reach will be the one that congress votes on in the end."

Supporters insist the TPP will level the playing field for US workers, and allow the country to help write the rules of 21st century global trade rather than its economic rival China.

Critics argue that the TPP maximises corporate profits, while killing US jobs and dismantling labour, environmental and safety standards.

Lawmakers inserted nearly 150 negotiating demands on the administration in their bill, mainly in intellectual property, labour law and the environment.

Senator Ron Wyden, the measure's chief Democratic co-author, said promotion of human rights will be made a formal part of the negotiation objectives for the first time.

Lawmakers have long complained that trade pacts are negotiated in absolute secrecy, but the bill would require Obama to publicise the TPP text 60 days before it is signed.