"It will help us to get more vessels in the water around the site of the collapse," Moore told a news conference.
The Port of Baltimore's shipping channel has been blocked since a fully loaded container ship lost power and collided with a support column on the Francis Scott Key Bridge last Tuesday, killing six road workers and causing the highway bridge which loops around Baltimore to fall into the Patapsco River.
The temporary channel opened on Monday (local time) has a controlling depth of 3.35 metres, freeing some commercial tugs and barges that had been trapped in the harbour, US Coast Guard Rear Admiral Shannon Gilreath told the news conference.
Gilreath said he did not know if those vessels carried goods or were empty and seeking to reload elsewhere.
The port is the largest in the US for "roll-on, roll-off" vehicle imports and exports of farm and construction equipment.
Recovery teams were working on opening a second temporary channel on the southbound side with a depth of 4.6 to 4.9m, Moore and Gilreath said. It could open "in the coming days," Moore said.
A third channel was planned with a depth of 6.1 to 7.6m that would allow almost all tug and barge traffic in and out of the port, Gilreath said.
But first the bridge debris needed to be cleared from the water, a task without an estimated timeframe, Gilreath said.
Some 50 recovery vessels were in the water working to clear debris and eventually free the cargo vessel stuck under steel bridge debris with 4000 containers and a 21-member crew aboard.
US President Joe Biden will travel to Baltimore on Friday and is expected to meet state and local leaders, including Moore, as he tours the damage area, White House spokesperson Karine Jean-Pierre said.
She said the administration had worked with local leaders to secure barges and a crane along with an early influx of money.
"As the president said within hours of the collapse, this administration will be with the people of Baltimore every step of the way," Jean-Pierre said.
She said the administration was working with Congress to ensure the federal government pays to rebuild the bridge.
