All three lanes of northbound traffic are now open on Interstate 295 in Portland.

The road had to be partially closed this afternoon when state engineers discovered a sinkhole developing under a culvert, according to Herb Thomson, a spokesman for the Maine Department of Transportation.

Thomson said the road should be fine for the evening commute, but crews plan to return after 9 p.m. to do more repairs. Eventually, the entire culvert will need to be replaced, he said.

Thomson said the road reopened to traffic around 3:35 p.m. During the closure, traffic backed up several miles.

4:32 p.m.

All but one northbound lane has been shut down on Interstate Route 295 near Tukey’s Bridge in Portland.

State Police said a sinkhole has developed in the area between Marginal Way Exit 7 and the bridge.

A Department of Transportation crew is on the scene making repairs.

Maine State Trooper Marvin Hinkley described the hole as five feet in circumference and four feet deep.

It opened up in the left lane. Maine DOT spokeswoman Meg Lane said the hole was the result of a failed culvert.

Northbound traffic at 2 p.m. was backed up past Deering Oaks Park and the University of Southern Maine. Delays were expected to continue into the evening.

Traffic officials have urged motorists to avoid the area.