Fijians have been warned if the Covid-19 triggered lockdown continues to be violated, the government will have no choice but to impose further restrictions.
Dozens of people have been arrested by police for breaching the lockdown rules in Lautoka city.
A nationwide curfew has been imposed in Fiji starting tonight.
Prime Minister Frank Bainimarama said the lockdown in Lautoka is scheduled to end on Friday.
"This week will prove absolutely critical in determining whether - come Friday morning - we lift restrictions or have to extend them. If even one of you fails to follow the rules, and God forbids this virus spreads within Lautoka, all of you will stay in lockdown even longer."
Mr Bainimarama said 100 police checkpoints have been erected around the country to monitor the situation.
He said the army and navy would assist police during the lockdown and curfew restrictions.
Mr Bainimarama said the curfew - from 10pm to 5am - should not impact shift workers including bakers, security officers and those in essential services.
He said those requiring medical assistance during the curfew would also be permitted to travel.
"But the main message for the vast majority of Fijians is that during 10pm and 5am, there is to be no wandering in the streets," he said.
"If you're caught out without a valid reason, you'll face serious consequences."