A member of the British Olympic team in Rio has been held up while enjoying a night on the town.

The news has caused deep shock among British athletes and officials – many of whom were looking forward to enjoying Rio’s nightlife after finishing their competitions. It has also led to an unprecedented warning to Team GB members that it is “not worth the risk” to leave the athletes village because of fears they might be targeted if they are seen wearing a British kit.

Reports of the incident, which happened in the early hours of Tuesday morning, spread quickly among athletes in Rio and there were unconfirmed reports that a weapon was involved, although Bill Sweeney, the BOA chief executive said: “I don’t believe a weapon, a firearm, was involved. It was a theft incident and the athlete is safe. It reiterates the need to be aware.”

It is understood the person in question was in shock but was not seriously hurt.

On Wednesday night British track and field officials responded to the news by sending an email to athletes warning them that if they left the village they would do so at their own risk.

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The letter told athletes that “following a significant security incident overnight,” they must follow a number of protocols, including not wearing Team GB kit out of the village and not taking taxis, for their own safety.

The letter, which has been seen by the Guardian, also warns athletes they must “avoid leaving the village after dark in anything other than British Olympic Association/Local Organising Committee/UK Athletics transport – taxis cannot be considered safe late at night. If you are planning on going out after dark and have no way of returning other than via taxi, do not go out.”

It also tells them of the dangers of going out on the town, and tells them they must inform officials before they go out.

“Do not go out of the village wearing TeamGB kit or carry anything of value unless absolutely unavoidable – this makes you too big a target for theft/crime,” it adds. “You MUST inform a member of team management if you are leaving the village and planning on staying out overnight – please do this BEFORE you leave.”

British athletes have also been told they must attend a BOA security briefing once they have finished competing. “This is absolutely essential – there are no excuses for not attending. If you can’t make the morning after you finish, go the morning after that – this is for your own safety.”

The letter then concludes by warning athletes that they might be better not going out in Rio because of the dangers of crime and theft.

“Rio is NOT a safe environment, and the level of crime has spiked in the last few days,” it adds. “Think very carefully about whether it is worth the risk of leaving the village to celebrate after you have finished competing – BOA/UKA staff cannot guarantee your safety when away from the village/British School/British House. Our strong advice is that it is simply not worth the risk given the current climate in Rio.”

British athletes have been told that other National Olympic Committees have put a curfew in place due to recent problems with security. The BOA has stopped short of doing this but the letter warns “if further safety/security issues arise it is likely that an outright ban on leaving the village after dark will be introduced”.

In a statement, the BOA said: “We can confirm there has been an incident of theft involving a Team GB athlete returning to their accommodation. All members of our delegation, including the individual concerned, are accounted for, and are safe and well.”