The evacuation fleet - the Linyi and another frigate, the Weifang, and the Weishanhu, a supply ship - was stationed near Yemeni waters before the airstrikes began.
The ships had been carrying out escort missions in the Gulf of Aden and Somali waters to protect Chinese and foreign vessels from pirate attacks.
The PLA navy ordered the ships to prepare for an evacuation mission, and on the night of March 26 it directed them toward the ports of Hodeidah and Aden, navy spokesman Liang Yang said on March 30.
Liang said the mission to evacuate Chinese citizens followed "the orders of President Xi Jinping and the Central Military Commission".
The Foreign Ministry "activated an emergency response mechanism" on March 26, Foreign Minister Wang Yi confirmed on March 28 on the sidelines of the Boao Asian Forum in Hainan province. "We actually have already started operations and those evacuated will be back home soon," he told reporters.
Zhu Jianping, an employee of CNBM International Engineering, arrived in Yemen two months before the evacuation, and heard "the sounds of gunshots and mortars every day".
"I was frightened, but I was reassured after the embassy informed me that the navy ship was coming," he told China National Radio when he arrived in Beijing on Wednesday.
At noon on March 29, the Linyi picked up 124 people - 122 Chinese and two foreign experts hired by Chinese enterprises - from Aden and arrived in Djibouti eight hours later.
The Weifang and the Weishanhu evacuated 449 Chinese nationals and six foreign employees of Chinese enterprises from Hodeidah before sailing to Djibouti.
Tian Qi, the Chinese ambassador to Yemen, said gathering the Chinese citizens together was "demanding" because they were dispersed in dozens of areas around the country.
The diplomat said security was a major concern for those who made the 230-kilometer trip from Sanaa to Hodeidah, as the mountainous road has seen serious outbreaks of violence.
Sound of gunfire
The evacuation was conducted under fire in some places, in particular near key infrastructure projects that were being fought over by the rebels and the government forces.
Aden has seen hundreds of people killed in what at times has been street-to-street fighting. Timing was of the essence to pick up the foreigners and, while any period of the day was dangerous, the fighting seemed less intense in the morning.
The Linyi docked at 10:15 am on Thursday, and although the fighting had subsided, the sound of gunfire and mortar explosions could still be heard.
Jiang Guoping, an officer with the PLA navy's 19th convoy fleet, told China Central Television, "We're learned that fire is exchanged more intensively in the afternoons and evenings."
Jiang said the evacuation had to be conducted quickly before the fighting escalated in the afternoon.
As if to confirm the danger, just 35 minutes after the evacuation began, a mortar shell explosion could be clearly heard nearby.
Zhou Yongsheng, a professor at the China Foreign Affairs University, said the success of the evacuation highlights the increasing experience of China's diplomatic missions and the growing international support for the country's humanitarian efforts.
Xinhua contributed to this story.
