A bicyclist was critically injured in a hit-and-run Thursday morning at Interstate 19 and West Ajo Way, authorities said.

A green Jeep Liberty was traveling east on Ajo shortly after 7 a.m. when it struck a bicyclist who was in a crosswalk at the southbound ramp to I-19, said Raul Garcia, a state Department of Public Safety spokesman.

The driver of the Jeep Liberty was last seen by witnesses headed south on I-19, Garcia said.

The Jeep Liberty is believed to be a 2005 to 2007 model. It has front-end damage and lost the grill in the crash, he said.

The bicyclist was taken to University of Arizona Medical Center for emergency surgery, Garcia said. The bicyclist suffered serious head injuries, he said.

Anyone with information is asked to call DPS at 746-4500.