More equipment and vessels arrive in final moments to attempt to save Titanic sub passengers

More rescue vessels arrived on Wednesday to assist crews in the major rescue operation of the Titanic-bound submarine that contains five passengers. 

Three vessels arrived “on scene” in the morning to join the search, according to a tweet from the U.S. Coast Guard’s First District.

There were more banging sounds detected earlier in the day from the remote North Atlantic Ocean, lifting hopes of those on the rescue mission, CNN reports.

The U.S. Coast Guard wrote on Twitter that a Canadian military surveillance "detected underwater noises in the search area" and that a robot was deployed to "explore the origin of the noises," but nothing was found. 

“We don’t know the source of that noise, but we’ve shared that information with Navy experts to classify it,” U.S. Coast Guard First District Commander Rear Admiral John Mauger told “CBS Mornings."

The OceanGate Titan submarine was reported missing on Sunday. The passengers have been identified as OceanGate CEO Stockton Rush, French mariner Paul-Henry Nargeolet, British businessman and explorer Hamish Harding, Pakistani businessman Shahzada Dawood and his son Sulaiman Dawood. 

The U.S. Coast Guard said on Tuesday that the sub will run out of breathable air around 5 to 6 a.m. Thursday EST. 

This is a developing story.