Hongkongers should avoid making any trips to Israel and Iran, the government warned on Thursday, raising the outbound travel alert to "black" for both countries.

The administration also advised residents who are in the two countries to leave or relocate immediately.

The black alert, which indicates severe threat, is the highest level on a three-tier system that also includes amber and red warnings. Two other countries with a black alert are Lebanon and Syria.

"Due to the highly unpredictable security situation in Israel and Iran, the [SAR] government advises Hong Kong residents to avoid all travel to Israel and Iran," a spokesperson said.

"Those already there should attend to personal safety and leave or relocate to relatively safe regions immediately."

Residents who require assistance may contact the Immigration Department or the Chinese embassy in the two countries, and the Security Bureau will continue to closely monitor the situation and issue updates.

A total of 19 Hongkongers have so far sought help, according to the Immigration Department. Sixteen of them have already managed to leave the area.

The latest conflict began when Israel launched a military attack on Iran, which led to retaliation by Tehran.