Canadian assets overheard "banging noises" in the search for the missing Titan submersible on multiple occasions over the past two days, authorities confirmed during a briefing Wednesday at the U.S. Coast Guard base in Boston.

The sounds were first registered Tuesday, and deep-sea remote-operated vehicles, or ROVs, "immediately" responded to the area, according to USCG Capt. Jamie Frederick. The data has been shared with the U.S. Navy for expert analysis.

Carl Hartsfield, a retired Navy captain and a scientist from the Woods Hole Oceanographic Institution, said during the briefing that the noises had been "described as banging," but authorities did not elaborate.

"I can't tell you what the noises are," Frederick said. "But what I can tell you, and I think that this is the most important point, is that we're searching where the noises are."

NEW ASSETS ‘ON-SCENE’ IN MISSING TITANIC SUBMARINE SEARCH AFTER CANADIANS PICK UP ‘UNDERWATER NOISES’

Bahamian research vessel, Deep Energy helping search for the submersible Titan

The Bahamian research vessel Deep Energy helps search for the submersible Titan on Tuesday. Titan contains a crew of five, including British billionaire Hamish Harding, who were due to visit the wreck of the Titanic. (U.S. Coast Guard/Cover Images)

The OceanGate Titan submersible is missing, along with five people on board: OceanGate CEO Stockton Rush; British businessman Hamish Harding, father-and-son Shahzada and Suleman Dawood, who are members of one of Pakistan’s wealthiest families; and Paul-Henry Nargeolet, a former French navy officer and leading Titanic expert.

Captain Jamie Frederick speaks to the press

U.S. Coast Guard Capt. Jamie Frederick speaks to reporters about the search efforts for the Titan submersible that went missing near the wreck of the Titanic, at Coast Guard Base in Boston on Wednesday. (Joseph Prezioso/AFP via Getty Images)

Naval and civilian assets from the U.S. and Canada expanded the search area to twice the size of Connecticut for a 21-foot submersible that could be trapped more than 3,800 meters below sea level at the ocean floor, Frederick said Wednesday.

ROV assets in the vicinity are capable of reaching as deep as 4,000 meters, he said.

Carl Hartsfield speaks to the press

Carl Hartsfield of the Woods Hole Oceanographic Institute talks about the noises heard during a U.S. Coast Guard update on the search efforts for five people aboard a missing submersible in Boston on Wednesday. (Scott Eisen/Getty Images)

"This is a search-and-rescue mission, 100%," he said.

WEATHER FORECAST FOR FINAL HOURS AS RESCUE CREWS WORK TO FIND MISSING TITANIC TOURIST SUBMERSIBLE

Hamish Harding poses for a photo

Hamish Harding is seen during the RMS Titanic Expedition Mission 5 on Sunday. (@actionaviation/Twitter)

The Coast Guard previously said that Canadian rescuers picked up "underwater noises" in the vicinity but would not confirm that they came from someone "banging" or "tapping." 

Authorities were still looking into the source of the sounds Wednesday morning, and at least five additional surface vessels are expected to join the effort by Thursday morning, along with additional ROVs.

Titan submersible being transferred onto a platform

This file image shows the Titan submersible being transferred onto a platform in the Bahamas. (OceanGate Expeditions)

SEARCH FOR MISSING TITANIC TOURIST SUB CONTINUES IN RACE AGAINST TIME

The Titan vanished Sunday during an attempt to visit the shipwreck of the Titanic about 900 miles east of Cape Cod.

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The crew had only an estimated 16 to 17 hours left of breathable air as of 1 p.m. Wednesday.