The city has issued a notice of violation against the owner of a property whose rock retaining wall collapsed onto Diamond Head Road, closing the thoroughfare for six hours Tuesday.

If the owner, identified as Allene H. Wong, does not repair or replace the wall on the Makalei Place property by May 13 as specified in the violation notice, an order could be issued and she could be fined $50 a day, said Curtis Lum, a spokes­man for the city Department of Planning and Permitting.

"All retaining walls 5 feet or more in height require approval of a licensed structural engineer," Lum said in an email. "A building permit will be required to replace or repair the wall."

Wong is believed to be traveling in Cuba, a relative told the Honolulu Star-Advertiser Tuesday.

City officials said she will also be billed the cost of the cleanup. A road labor supervisor at the scene said the wall is believed to have been built in the 1920s, and apparently without rebar.

It’s unclear, however, what triggered the wall’s collapse.

Police got the initial call at 1:42 p.m. Tuesday and traffic was contraflowed in the area until 3:25 p.m., when Diamond Head Road was shut down completely from Coconut Avenue to the Diamond Head Lighthouse to allow a crew from the city Department of Facility Maintenance’s Road Division to clear the road of debris.

The road was reopened at 9:16 p.m.

No one was injured, nor were any vehicles damaged by the wall’s collapse, despite the scenic road’s popularity among motorists, bicyclists and pedestrians.