A leading US brokerage has increased its fourth quarter loss estimates for General Motors and Ford in light of "a fundamentally altered credit environment".

JP Morgan Secutities said simultaneous weakness in North America and Europe, including a potential 15% fall in western European auto sales in 2009, would make 2009 difficult, according to Reuters.

"General Motors and Ford are both likely to survive, but we now see a higher '09 cash burn rate," the brokerage said.

Reports this week have highlighted growing analyst concern at the Detroit automakers' cash burn estimated at US$1bn a month, despite strenuous efforts by Ford and GM to reduce costs.

The brokerage increased GM's 2008 loss estimate to $21 a share from $20.25 a share, and the 2009 loss estimate to $16.25 a share from $11 a share, the report said. Ford's loss was seen widening to $3.20 a share from $3 in 2008 and to $1.90 loss per share from $0.95 next year.

JP Morgan also reduced its earnings estimates on US auto parts suppliers and downgraded four companies in its coverage, noting that double-digit production declines on both sides of the Atlantic next year may result in considerable balance sheet stress, Reuters added.