Canadian oil giant Enbridge has doubled the manpower and equipment for a cleanup operation after more than three million litres of oil spilled into Michigan's Kalamazoo River, one of the state's major waterways.

The leak was detected Monday in a pipeline that carries about 30 million litres of oil daily from Griffith, Ind., to Sarnia, Ont.

The 76-centimetre pipeline was built in 1969 and is operated by Enbridge Energy Partners LP of Houston, an affiliate of Calgary-based Enbridge Inc.

Associated Press reporter Tim Martin said Wednesday the company has "doubled its manpower today and doubled the amount of booms and vacuums that are sucking up oil on the river."

"(Company officials) have appeared pretty confident from the start that they would be able to stop the flow of oil well before it reaches Lake Michigan," Martin told CTV News Channel in a telephone interview from Battle Creek, Mich.

"They feel they'll be able to stop it in Kalamazoo County, which is quite a few miles before it feeds into southern Lake Michigan."

Company officials estimated Wednesday that about 3,100,252 litres of oil was spilled into Talmadge Creek before the leak was repaired. However, state officials reported Tuesday evening that during a briefing with the company, Enbridge said about 3,319,806 litres of oil was spilled.

The oil then flowed into the Kalamazoo River and Morrow Lake. Mary Dettloff of the Michigan Department of Natural Resources said the spill has impacted about 56 kilometres of the Kalamazoo River. A state of emergency has been declared in Calhoun County and other potentially affected areas.

Dettloff told CTV News Channel Wednesday evening that valves have been shut off on either side of the leak, so petroleum is no longer flowing through the pipe.

Dettloff said the agency has yet to undertake an assessment of the environmental damage due to high levels of toxic fumes in the air around the spill. She said she expects that effort to get underway Thursday.

Earlier Wednesday, Enbridge officials came under fire for an apparent delay in reporting the spill. Rep. Mark Schauer of Michigan released documents that show the spill was not reported to the National Response Center until 1:30 p.m. on Monday. Enbridge said the spill was detected at 10:30 a.m., but had to determine the estimated volume of the spill before reporting it to authorities. The company said it tried calling at 1:00 p.m. but was put on hold and so called back a half hour later.

Enbridge president and chief executive Patrick D. Daniel said Wednesday the company has "made significant progress" during the cleanup effort so far but still has "a long way to go."

Daniel said Tuesday evening crews were digging up the pipe to find out what caused the leak.

The company had about 200 people working on the spill on Tuesday and said it will set up a centre to help ducks, geese and other animals coated with oil. The U.S. Environmental Protection Agency was also scheduled to bring additional workers to the region.

Health officials have warned area residents to stay away from the spill. A few households have been evacuated.

Martin said many local residents were surprised to learn there was a pipeline so close to the river.

"A lot of people don't realize that in the industry that's not all that uncommon," Martin said. "I think it just took a lot of people that actually live in this area by surprise that there's been a pipeline there since 1969 and there's oil close by every day."

According to Martin, company officials have yet to issue a timeline or a cost breakdown for the cleanup.

Groundwater testing was also scheduled to begin Wednesday to ensure water supplies close to the river had not been contaminated. Calhoun County officials said they are unconcerned about the water systems supplying Marshall and Battle Creek.