The investigation and cleanup were continuing on the long Canada Day weekend following Friday's derailment of as many as 46 CN Rail cars in the St. Clair Tunnel.
One tank car containing sulphuric acid was breached in the tunnel but contamination was contained.
Port Huron, Michigan CAO James Freed posted an update on Twitter Sunday afternoon.
Sunday 6/30/19 Status Update. pic.twitter.com/BSQmO3EKaw
— James Freed (@JamesFreed) June 30, 2019
The Transportation Safety Board of Canada (TSB) and the United States National Transportation Safety Board (NTSB) deployed teams of investigators to the site.
"Investigators from both agencies are working to determine the point of derailment," the TSB said in a news release Saturday. "If the point of derailment is in Canada, the TSB will become the lead agency for the accident investigation."
The TSB said access to the site is restricted due to the limited space available and the potential hazards in the tunnel, adding it must ensure that the site is safe for investigators and those working to clear the accident site.
The process of removing damaged rail cars was ongoing.
There is no indication as to how long it will take to reopen the rail tunnel that runs under the St. Clair River between Sarnia and Port Huron, Michigan.
No one was injured in the derailment that occurred early Friday morning.
Sarnia Fire & Rescue responded at 5:30 a.m.