BEIJING — A railway bridge under construction in northwest China’s Qinghai province collapsed early Friday, killing at least 12 workers and leaving four others missing, according to state media.

The accident occurred around 3 a.m. when a steel cable snapped during a tensioning operation on the 1.6-kilometer (1-mile) span, which crosses the Yellow River. Sixteen workers were on the bridge at the time.

Aerial photos released by Xinhua News Agency showed a large section of the bridge’s aquamarine arch missing, with part of the deck bent downward into the river.

Search efforts for the missing workers have deployed boats, a helicopter, and remotely operated robots.

The bridge deck stands about 55 meters (180 feet) above the river, the China Daily newspaper said. Authorities have not released details about the cause of the collapse, and investigations are underway. — Agencies