A Russian swimmer went missing during Istanbul’s annual cross-continental Bosphorus race, with officials confirming Monday that his tracking chip showed no record of him leaving the water.

Authorities identified the missing participant as 30-year-old Nikolai Svechnikov, a professional swimming coach, who began the 6.5-kilometre race from Kanlica on the Asian side to Kurucesme on the European side, along with more than 2,800 swimmers from 81 countries.

The Turkish Olympic Committee, which organised the event, confirmed his disappearance, while the Istanbul governor’s office said security footage and chip data showed Svechnikov started but never reached the finish line.

By late Monday, there was still no sign of him, prompting Istanbul prosecutors to launch a formal investigation, according to local media reports.

There was still no trace of him late Monday, with Istanbul prosecutors opening an investigation into his disappearance, the private DHA news agency reported.

Russia’s consulate general in Istanbul said it was in contact with Turkish authorities about the situation and confirmed Svechnikov’s relatives had been informed.

According to the official race website, swimmers have a time limit of two hours to complete the course, with the coast guard picking up anyone who does not finish within that time.

The Olympic Committee said the race began at 10:04 am (0704 GMT) with the last swimmer entering the water at 10:54 am.

After the two-hour race limit finished, an initial check found that three swimmers were missing, but this was later reduced to a single athlete, it said.

“This information was immediately shared with the coast guard command, the maritime police department, and the Istanbul governor’s office, and search and rescue operations were … immediately initiated,” it said.

“We are working in full cooperation with the coast guard and police units to shed light on the incident.”