Ora called the party, which took place on Saturday in Notting Hill, west London, a "serious and inexcusable error of judgement."
British pop star Rita Ora apologises after she admitted she had attended a party to celebrate her 30th birthday which broke England's strict Covid-19 lockdown laws.
Ora said she had gone to a "small gathering with some friends" which the Sun newspaper said was held at a restaurant in west London on Saturday night with 30 people in attendance.
Under the lockdown rules, people in England are not allowed to mix with other households indoors and can meet one person outside. Restaurants have been closed except for takewaways to prevent the spread of the coronavirus.
"It was a spur of the moment decision made with the misguided view that we were coming out of lockdown and this would be OK," Ora said in a statement on Instagram Stories.
"I’m deeply sorry for breaking the rules and in turn understand that this puts people at risk. This was a serious and inexcusable error of judgement. Given the restrictions, I realise how irresponsible these actions were and I take full responsibility."
Police said officers had been called to reports of breach of Covid rules but had not found any offence being committed.
"Officers continue to assess the allegations and are liaising with the local authority regarding a potential breach of regulations at the premises," police said in a statement.
The BBC reported that Ora was voluntarily paying a fine.
The singer of hits that include "Let You Love Me" and "How to Be Lonely" has volunteered to pay a fine.
Police in England can issue fines of up to £10,000 ($13,352, €11,168) for breaches of the lockdown curbs.
England was placed under four weeks of restrictions to stop the spread of coronavirus in November. Restaurants and pubs were among businesses affected.
Individuals were also banned from meeting indoors with people from other households.
The lockdown is set to end on December 2 and be replaced by a tiered system allowing hospitality venues to reopen in certain areas under social distancing rules.
The Sun newspaper published photos of Ora and other celebrities arriving at a restaurant.
"It's important that everybody in society sets an example by following the rules – that is for every member of the public, including celebrities," the prime minister's official spokesman said.
"But it's up to police to decide what action to take."
READ MORE: Latest coronavirus updates