A-shares in the petroleum and petrochemical sector experienced a sudden surge during afternoon trading. Blue Flame Holdings saw its stock price jump directly to the daily limit.

On April 13, after opening higher but trending lower in the morning session, the A-share petroleum and petrochemical sector abruptly rallied in the afternoon.

Among individual stocks, Blue Flame Holdings hit the upward trading limit in a straight-line move during the afternoon, reaching 10.18 yuan per share.

Other stocks including Intercontinental Oil & Gas, Zhunyou Oilfield Services, and Tongyuan Petroleum also showed strong upward momentum in the afternoon.

The market movement follows reports that, in the early hours of April 13 Eastern Time, the U.S. President announced on his personal social media platform that the United States would impose a blockade on vessels entering or leaving Iranian ports, effective at 10 a.m. Eastern Time on April 13.

According to British sources, following the U.S. President's announcement of the blockade on the Strait of Hormuz, all traffic through the strait has ceased.

The blockade is reported to have already lasted for several hours. Prior to the announcement, the number of oil tankers passing through the Strait of Hormuz had seen a slight increase on April 11. Although shipping volume decreased on April 12, passage remained possible. However, after the blockade was declared, all traffic appears to have stopped, with at least two vessels that were exiting the strait having turned back.

In response to the U.S. threat, Iranian military officials warned that any military vessel attempting to approach the Strait of Hormuz under any pretext would be considered a violation of the ceasefire agreement and met with a severe response.

On April 12, Iran's Islamic Revolutionary Guard Corps issued a statement indicating that the Strait of Hormuz is currently under control and remains open to non-military vessels, provided specific regulations are followed.

A report by The Wall Street Journal on April 12, citing Farzin Nadimi, a scholar at the Washington Institute for Near East Policy, noted that despite U.S. claims of having inflicted devastating blows on the Iranian navy, over 60% of the Islamic Revolutionary Guard Corps' fast-attack vessels remain operational. These small craft are well-suited for operations in narrow waters and are harder to detect by satellite compared to larger ships.

The U.S. Central Command claimed that as of April 6, more than 155 Iranian vessels had been sunk, most belonging to Iran's conventional navy. Chris Long, a former British naval officer, suggested that Iran may have hidden hundreds of small attack craft along its rugged coastline.

Vivek Dhar, an analyst at Commonwealth Bank of Australia, stated in a report that the U.S. threat to blockade the Strait of Hormuz could further escalate conflict in the Middle East. A blockade directly endangers Iran's oil exports through the strait, which amounted to approximately 1.7 million barrels per day last month. Consequently, such a move could tighten physical crude and refined oil markets further. The scarcity of spot oil is already reflected in physically delivered oil benchmarks and may drive oil prices above $140 per barrel in the coming weeks.