(Adds detail, Lam comment)

HONG KONG, July 13 (Reuters) - Hong Kong will tighten socialdistancing measures again from Wednesday amid growing worriesabout a third wave of coronavirus infections, Chief ExecutiveCarrie Lam said.

The government will limit group gatherings to four people-from 50 - a measure last seen during a second wave in March.

Twelve types of establishments, including gyms and gamingcentres, must shut down for a week. Restaurants will only beallowed to give out takeaway after 6.00 p.m.

The Chinese-ruled city recorded 52 new cases of coronaviruson Monday, including 41 that were locally transmitted, healthauthorities said. Since late January, Hong Kong has reported1,522 cases and local media reported an eighth death on Monday.

"Unless we have an effective vaccine which can be widelyused in the community, we may need to co-exist with the virusfor a period of time," Lam told a news conference on Monday.

The measures were the result of a three-way tug of warbetween considerations related to public health, economic impactand social acceptability, she said.

Lam also said civil servants will work flexible hours andthat wearing face masks will be mandatory on public transport.

Earlier on Monday, the organiser of the Hong Kong Book Fair,which draws about one million visitors annually, said the eventdue to start on Wednesday will be postponed to a later,unspecified date due to the coronavirus. L3N2EK14S

At least three other July fairs and expos were alsopostponed.

Hong Kong's Education Bureau on Friday announced thesuspension of all schools from this week. urn:newsml:reuters.com:*:nL4N2EH1GK

(Reporting by Donny Kwok, Yanni Chow and Carol Mang; Writing byMarius Zaharia; Editing by Alex Richardson and Angus MacSwan) ((marius.zaharia@thomsonreuters.com; +852 2843 6358; ReutersMessaging: marius.zaharia.thomsonreuters.com@reuters.net))