PORTLAND — The southbound lanes of Interstate 295 have been shut down in the wake of a one-vehicle crash near the Back Bay, police said.

Department of Public Safety spokesman Stephen McCausland said a southbound minivan struck a guardrail around 1 p.m.

Two children, a boy and a girl who are elementary-school age, were thrown from the vehicle and were transported to Maine Medical Center with serious injuries, McCausland said. The injuries aren’t believed to be life-threatening, he said.

A man and woman in the vehicle suffered minor injuries. The names of the victims were not immediately disclosed.

Southbound motorists are advised to seek alternate routes, such as the Maine Turnpike or Route 1. McCausland said troopers hope to have the scene cleaned up by 4:30 p.m.