Swine-flu-ridden Mexico has heightened alert and ordered to shut down schools nationwide, Health Secretary Jose Angel Cordoba said on Monday.

The government decided to extend an earlier order to close schools in some of its 32 states and the capital city to all schools nationwide.

The suspension of schools, ranging from universities to kindergartens, is expected to last till May 6.

Cordoba told a news conference late Monday that the death toll from confirmed or suspected swine flu cases has risen to 152.

Officials said most of the people who were killed in the flu epidemic are adults aged from 20 to 50. No cases of children have been reported yet.