* Further curbs could lead to need for additional liquidity

* HY pretax loss of $1.64 billion

* Shares down 17%

Sept 24 (Reuters) - Cineworld, the world's second-biggest cinema operator, warned on Thursday it might need to raise more money if theatres shut again from fresh pandemic curbs after it swung to a $1.64 billion first-half loss, sending shares down 17%.

The Regal cinema owner, which counts United States as its largest market, said it was in talks with lenders to avoid an impending loan default, and flagged survival risks as studios delay major releases and people stay away from theatres. "If governments were to strengthen restrictions on social gathering..., it would have a negative impact on our financial performance," the British company said.

New curbs could be a major setback after Cineworld reopened 561 out of 778 sites, highlighted the strong performance of Christopher Nolan's "Tenet", and said it was looking forward to other big releases.

"Two more big name films, West Side Story and Black Widow, have been pushed back to 2021," AJ Bell analyst Russ Mould said.

"There isn't anything out now or coming very soon that will really make people want to take the risk of sitting in a room with a load of strangers."

FIGHTING TO STAY RELEVANT

The world's largest cinema chain AMC and Universal Pictures have agreed the studio's movies would be made available to U.S. audiences at home after three weekends in cinemas.

Cineworld boss Mooky Greidinger, however, said his company would stick with the traditional script.

"Our policy regarding the theatrical window remains unchanged as an important part of our business model, and we will continue to only show movies that respect it," he said in a statement.

A model agreed by AMC and Universal could easily be replicated across the industry, eToro analyst Adam Vettese said. Cineworld will have to either go on a charm offensive with other studios or make sure this shift does not result in lost revenues, he said.

The landscape could be further changed by a U.S. ruling last month which allows movie studios to own theatres.

"The more likely candidates to enter the theatrical space would be streamers such as Netflix or Amazon, who are looking to attract renowned film makers with the prospect of a theatrical release," Third Bridge analyst Harry Barnick said.

Another challenge for Cineworld is its tussle with Canada's Cineplex, suing the British group for damages after it scrapped a $1.65 billion takeover.

Cineworld has made a counter-claim against Cineplex.

(Reporting by Tanishaa Nadkar in Bengaluru, Editing by Sherry Jacob-Phillips, Saumyadeb Chakrabarty and Tomasz Janowski)