Authorities in east China are racing to find a missing 9-year-old girl who was last seen in the company of two adults found dead on Sunday.

In a weeklong disappearance, the mystery of missing Zhang Zixin has gripped China on Friday with a 20,000 yuan, or $3,951, reward offered as part of an urgent appeal for information about the missing child.

Live videos streamed by state-run media outlet Beijing News showed search crews on speedboats deploying sonar equipment as they tried to detect signs of her in caves and waters along the East China Sea, near Xiangshan County in the eastern province of Zhejiang. Search teams said they may be utilizing drones as well.

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Zhang, a second-grader with a long ponytail and glasses, was last seen on security footage around 7:30 PM on Sunday. She appeared on a road far from her home in Hangzhou with her family’s tenants - a middle-aged couple who said they were taking her to a wedding in Shanghai.

Another surveillance camera in the area caught the couple almost three hours later, but Zhang was nowhere to be seen. Local officials stated Wednesday the man and woman, both from the southern province of Guangdong, drowned themselves in a nearby lake that night.

Zhang’s government services card was found in a pavilion along the Xiangshan coast on Wednesday night, according to authorities, and a 6-mile search zone was announced.

“The girl is about [4 feet and 3 inches] tall, a bit rounded, has long hair in a ponytail and red-framed glasses,” the announcement said. “According to surveillance camera footage, Zhang was last seen with [the couple] on July 7 in front of the Golden Coast Hotel in Xiangshan township, Ningbo. She was wearing a white top and green skirt, grey sandals and has not been seen since.”

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In an interview with Chinese state-run publication Dushi Kuaibao, the girl’s father, Zhang Jun, said the tenants deceived his senile farmer parents into letting them take Zixin away. He said his parents were caring for her while Jun was working in a northern Chinese city hundreds of miles away.

Jun recalled how the tenants claimed to want to make Zixin a flower girl at a wedding in Shanghai and despite his objections, led the girl away the following morning. For three days he was able to stay in contact with the couple via WeChat, China’s most popular social media platform, They promised to bring the girl home by the end of July 6 and sent frequent updates; Jun said everything seemed “normal” initially.

He grew increasingly suspicious, however, and finally took an overnight train home last Saturday when the couple refused his offer to drive to their location to pick Zixin up, switching their phone off shortly afterward. He said he spoke to his daughter for the last time on Sunday.

Jun reported his daughter’s missing report to authorities on Monday morning, posting the couple’s information online the next day. After officials confirmed the deaths of the couple, Zixin’s whereabouts became a nationwide fixation.

State media outlets provided continuous coverage on the girl, with journalists flocking to the hometowns of the subjects to uncover details. Additionally, Hangzhou police sent a task force to Guangdong as part of their ongoing investigation.

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By midday Friday, however, prospects of finding Zixin – alive or dead – dwindled as the search operation ended amid rainy weather and choppy waters.

Fox News' Morgan Cheung contributed to this report.