HONG KONG — Rescuers were searching Monday for crewmen missing from an Iranian oil tanker that had collided with another ship off China’s coast, leaving the tanker in flames and at risk of exploding and sinking, the Chinese authorities said.

The Panamanian-flagged tanker, the Sanchi, collided with the CF Crystal, a Hong Kong-registered bulk freighter, around 8 p.m. Saturday about 160 nautical miles east of Shanghai. That area of the East China Sea is frequently crossed by ships traveling to China, South Korea, Taiwan and Japan.

All 21 Chinese crew members of the CF Crystal, which was transporting grain from the United States to Guangdong Province in southeastern China, were rescued, China’s Ministry of Transport said. But the Sanchi’s entire crew — 30 Iranians and two Bangladeshis — were missing after the collision. One body has been recovered, Iran’s Ports and Maritime Organization said Monday.

Four Chinese government ships, two pollution control vessels, four commercial vessels, several fishing boats and a South Korean Coast Guard ship were aiding the search.