An accident on Interstate 93 near Assembly Square in Somerville caused authorities Friday afternoon to close down the high-speed lanes in both the northbound and southbound directions, according an alert sent by Massachusetts State Police.

According to WBZ News Radio (1030 AM), by around 4:30 p.m. the accident was cleared, but the incident caused heavy traffic.

The radio station said the accident occured in the left lane of I-93 northbound.

Based on scanner radio transmissions, the highway accident happened sometime around 3:30 p.m.

Somerville, Medford and Boston fire departments responded to the accident, according to scanner trasnmissions.

WBZ reported at 4:33 p.m that the accident has caused a massive nine-mile backup on I-93 northbound leading into Boston. 

Somerville Patch will update this story when more information is available.