Two Sydney high schools in lockdown

Two high schools in Sydney's southwest will remain open and students are set to return a day after they went into lockdown over social media threats.

Two southwest Sydney schools have been placed in lockdown after receiving threats via social media. (AAP)

Students will return to two high schools in southwest Sydney a day after they went into lockdown over social media threats.

Police attended East Hills Boys High School in Panania and Sir Joseph Banks High School in Revesby on Tuesday but refused to detail the timing and content of the threats.

Parents were advised their children were safe but had the option of picking them up from the neighbouring schools, a NSW Department of Education spokesman said in a statement.

Since the terror-related murder of police accountant Curtis Cheng on October 2, there have been countless threats made against major Sydney sites.